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M  * 

LIBRARY 

OF    THE 

UNIVERSITY  OF  CALIFORNIA. 


I 


Electric  Furnaces  and  their  Industrial 
Applications 


ELECTRIC  FURNACES  AND 

THEIR  INDUSTRIAL 

APPLICATIONS 


J.    WRIGHT 
it 


WITH   57    ILLUSTRATIONS 


or  THE   ^ 


UNIVERSITY 


NEW   YORK 
THE    NORMAN    W.    HENLEY    PUBLISHING    CO 

132    NASSAU    STREET 


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INTRODUCTION 

THE  development  of  the  electric  furnace,  and  the  various 
industries  with  which  it  is  associated,  as  a  necessary  auxiliary 
to  the  processes  involved,  is  making  vast  strides,  and  is 
regarded  with  ever-increasing  interest  by  the  electro- 
chemist  and  metallurgist,  who  see  in  it  possibilities,  far 
beyond  those  offered,  until  some  few  years  back,  by  the  blast 
furnace  on  a  commercial  scale,  and  the  oxy-hydrogen  flame 
in  the  laboratory. 

The  limitations  of  temperature  imposed  by  the  methods 
available  prior  to  the  introduction  of  electricity  as  a  heating 
agent,  were  such  as  to  render  commercially  impossible 
many  of  the  processes  now%carried  out  by  its  aid.  On  the 
other  hand,  the  introduction  of  the  electric  furnace  with  its 
vast  possibilities  in  the  field  of  exceedingly  high  tempera- 
tures, gave  rise  at  first  to  misuse  of  the  power  available  ; 
i.e.  the  temperatures  required  for  the  various  reactions  were 
over,  rather  than  under  estimated,  and,  as  a  result,  the  sub- 
stances which  should  have  'been  produced  by  the  furnace 
were  again  split  up  into  constituent  elements,  or  built  up 
into  compounds  other  than  those  which  it  was  originally 
intended  to  produce.  Many  of  the  early  failures  were  due 
to  this  cause,  especially  in  furnaces  of  the  "arc"  typey 
but  experience  has  taught  the  usual  lesson,  and  it  is  now 
possible  to  regulate  the  temperature  of  an  electric  furnace 
within  far  narrower  limits  than  is  possible  with  furnaces  of 
the  ordinary  type,  consuming  coke  and  coal  fuel. 

There  is  hardly  an  electro-metallurgical  process  to  which 
the  electric  furnace  has  not  been  applied,  either  experi- 


INTRODUCTION 

mentally,  or  on  a  commercial  scale,  and,  though  many  of  the 
experimental  attempts  have,  thus  far,  proved  abortive,  the 
success  of  the  remainder  justifies  the  hope  that  perseverance, 
aided  by  the  incentive  to  progress  in  the  shape  of  much 
valuable  material,  such  as  low-grade  ores,  so-called  "  waste 
products,"  etc.,  at  present  unworkable,  may  lead  to  increased 
research  in  this  promising  field,  in  which  it  is  fairly  safe  to 
predict  that  the  indefatigable  worker  will  not  go  unrewarded. 
The  introduction  of  acetylene  gas  for  illuminating 
purposes,  has  of  course,  been  responsible  for  the  great 
advance  in  the  carbide  industry,  which  at  present  con- 
stitutes the  largest  branch  of  electric  furnace  work, 
although  at  one  time  the  boom,  and  consequent  over 
production,  threatened  ruin  to  many  works.  So  great,  in 
fact,  was  the  reaction  consequent  upon  an  overstocked 
market,  that  many  factories  possessing  furnaces  and  plant 
for  the  manufacture  of  calcium  carbide,  turned  their  atten- 
tion to  other  substances,  which,  with  a  little  adaptation, 
their  furnaces  could  be  made  to  produce.  Alloys  of  the 
ferro-chrome  type  are  amongst  the  substituted  products, 
being  largely  used  in  hardening  armour  plates,  etc. 

Electric  smelting  furnaces  for  the  reduction  of  iron  and 
other  ores  to  the  metallic  state,  have  also  provided  a  subject 
for  extensive  research,  with  no  small  measure  of  success,  it 
having  been  found  possible  to  apply  the  electric  smelting 
process  in  many  cases  where  the  blast  furnace,  either  from 
scarcity  of  fuel  or  similar  causes,  was  out  of  the  question. 

It  is  naturally  impossible  at  the  present  stage  of  our 
knowledge  concerning  the  generation  of  electrical  energy 
from  coal  and  other  fuels,  for  the  electric  smelting  furnace 
to  compete  with  smelting  furnaces  using  fuel  direct,  but 
there  are  many  instances  in  which  the  electrical  process 
can  be  introduced  with  advantage,  and  a  fair  promise  of 
profit  to  the  metallurgist. 

Metalliferous  ores  frequently  abound  in  localities  where 
fuel  of  any  description  is  scarce,  but  water  power  plentiful ; 


INTRODUCTION 

in  such  cases,  a  hydro-electric  generating  plant,  though 
expensive  to  instal,  frequently  provides  a  ready  way  out  of 
the  difficulty.  Water  power  has,  in  fact,  been  the  salvation 
of  the  electro-chemical  and  electro-metallurgical  industries 
which  for  the  greater  part  involve  a  vast  expenditure  of 
power  within  a  comparatively  small  compass.  Hence  we 
find  almost  all  the  large  works  concerned  in  the  foregoing, 
allied  industries,  confined  to  America  and  the  Continent, 
and  frequently  to  localities  where  fuel  is  comparatively 
scarce  but  water  power  plentiful. 

Niagara,  with  its  50,000  H.P.  derived  from  the  celebrated 
Falls,  is  a  case  in  point,  and  it  is  worthy  of  note  that  by  far 
the  greater  proportion  of  this  huge  power  is  utilized  in  the 
two  industries  enumerated  above. 

It  is  unnecessary  to  enlarge  further,  at  this  point,  upon  the 
many  applications  of  the  electric  furnace  in  modern  in- 
dustry, in  that  the  various  processes  will  be  alluded  to  iifc 
connexion  with  the  several  furnaces  to  be  described  later, 

There  is  also  a  type  of  furnace  which  the  author  proposes 
to  include  in  this  work,  with  the  object  of  rendering  it 
complete,  and  that  is  the  electrolytic  type.  Although  not, 
strictly  speaking,  furnaces,  in  the  ordinary  acceptation  of 
the  term,  there  are  several  forms  of  apparatus  which  depend 
for  their  action  on  a  combination  of  thermal,  electrolytic,  and 
chemical  effects.  Since  the  office  of  the  furnace  proper, 
viz.,  that  of  heating  the  raw  materials,  is  an  essential 
auxiliary  in  such  cases,  it  has  been  resolved  to  include  them 
in  the  pages  which  follow,  the  necessary  line  of  demarcation 
between  a  thermal  and  an  electrolytic  process  pure  and 
simple  being  determined  by  the  presence  of  an  aqueous 
solution.  Only  such  methods  and  apparatus  will  be  dealt 
with  as  involve  the  presence  of  a  fused  electrolyte. 

Several  of  the  types  of  electric  furnace  construction,  de- 
scribed in  detail  in  the  pages  which  follow,  have  never  pro- 
gressed beyond  the  experimental  stage.  Their  descriptions 
are  included  with  a  view  to  showing  the  extraordinary 


INTRODUCTION 

amount  of  ingenuity  which  has  been  expended  upon  electric 
furnace  design,  with  a  view  to  rendering  them  efficient,  and, 
as  far  as  possible,  automatic  in  action.  It  is  this  very 
ingenuity,  entailing  a  certain  elaboration  of  detail  which 
has  militated  against  the  commercial  success  of  several 
very  promising  furnace  inventions.  To  put  the  matter  in 
a  nutshell,  the  aspiring  designers  of  some  electric  furnaces 
have  attempted  to  apply  principles  of  construction  and 
operation  comparable  with  the  delicate  mechanism  and 
controlling  principles  of  the  self -regulating  arc  lamp. 

It  is  obviously  a  mistaken  feature  in  electric  furnace 
design,  this  elaboration  of  detail.  In  an  apparatus  whose 
parts  may  be,  and  frequently  are,  subjected  to  extremely  high 
temperatures,  it  is  necessary  that  every  part  shall  possess 
stability,  in  order  to  resist  the  destructive  tendency  of  such 
great  heat,  a  stability  which  the  nature  of  some  of  these 
inventions,  renders  impossible  of  attainment. 

The  illustrations  in  this  book  are  essentially  in  the  nature 
of  sectional  diagrams,  representing  "  principles  of  construc- 
tion "  rather  than  views  of  the  objects  as  they  actually 
appear  to  the  observer.  Photographs  of  the  majority  of 
electric  furnaces  would  convey  little  or  no  information  to 
the  reader ;  a  mass  of  brickwork,  with  perhaps  some  iron 
plates ;  a  series  of  heavy  cables  leading  in ;  and  one  or  two 
flues  for  carrying  off  the  gaseous  products  :  that  is  all. 

J.  W. 


viii 


SUMMARY  OF    CONTENTS 

SECTION    I  PAGES 

HISTORICAL  AND  GENERAL 1-20 

SECTION   II 
ARC  FURNACES     .......         .         .       21-26 

SECTION   III 
RESISTANCE  FURNACES  AND  TYPICAL  PROCESSES    .         .       27-57 

SECTION    IV 

CALCIUM  CARBIDE  MANUFACTURE          .  .         .       58-106 

SECTION    V 

IRON    AND     STEEL     PRODUCTION     IN     THE    ELECTRIC 

FURNACE 107-164 

SECTION    VI 

PHOSPHORUS      MANUFACTURE      IN      THE       ELECTRIC 

FURNACE  .  165-169 

SECTION    VII 
GLASS  MANUFACTURE  IN  THE  ELECTRIC  FURNACE         .     170-175 


SUMMARY  OF  CONTENTS 

SECTION   VIII  PAGES 

ELECTBOLYTIC  FURNACES  AND  PROCESSES     .          .          .     176-213 

SECTION    IX 

MISCELLANEOUS    ELECTRIC  FURNACE  PROCESSES  .     214-220 

SECTION    X 
LABORATORY  FURNACES  AND  EXPERIMENTAL  RESEARCH     221-234 

SECTION   XI 
TUBE  FURNACES  *         .          .          .          .          .          .     235-245 

SECTION    XII 
TERMINAL  CONNEXIONS  AND  ELECTRODES       .         .         .     246-256 

SECTION   XIII 
EFFICIENCY     AND     THEORETICAL     CONSIDERATIONS       .     257-264 

SECTION   XIV 
MEASUREMENT    OF    FURNACE    TEMPERATURES  265-283 


•f\8  R  A 
OF  THE 

{   UNIVERSITY  } 


SECTION   I 

HISTORICAL  AND  GENERAL 

Definition.—  Strictly  speaking,  an  electric  furnace  is  an 
apparatus  for  bringing  about  a  physical  or  chemical  change 
in  materials  by  the  aid  of  heat  obtained  from  the  transforma- 
tion of  electrical  energy.  There  is,  however,  another 
class  of  apparatus,  which  the  writer  has  seen  fit  to  include, 
under  the  title  "  Electrolytic  Furnaces,"  in  which  the  action 
is  in  part  electro-thermal,  as  in  the  electric  furnace  pure  and 
simple,  and,  for  the  rest,  electrolytic.  This  class  of  furnace 
is  mainly  employed  for  the  electrolysis  of  fused  salts,  as, 
for  instance,  in  the  manufacture  of  aluminium,  where  heat 
is  a  necessary  auxiliary  if  the  requisite  fusion  of  the  electro- 
lyte is  to  be  maintained. 

Historical.  —  As  early  as  1853  a  form  of  arc  furnace  con- 
struction, devised  by  Pichon,  was  described  in  the  Practical 
Mechanics'  Journal.  It  consisted  of  a  series  of  arcs,  set  up 
between  electrodes  of  large  size,  and  through  the  several 
independent  heat  zones  of  which,  metallic  ores,  mixed  with 
carbon,  were  passed,  with  the  object  of  reduction.  There 
is  no  record  of  such  a  furnace  having  ever  existed,  except  on 
paper. 

Sir  William  Siemens  may  justly  be  credited  with  having 
been  the  first  to  suggest  the  employment  of  electric  furnaces 
on  a  commercial  scale.  For  some  time  (1878-1879)  he 
conducted  experiments,  with  a  view  to  determining  the 
possibilities  of  the  arc  furnace  as  an  auxiliary  to  certain 
industrial  processes,  and  in  June,  1880,  embodied  the  results 
of  his  researches  in  a  paper  which  he  read  before  the  then 


ELECTRIC    FURNACES    AND 

Society  of  Telegraph  Engineers.  In  the  course  of  his  experi- 
ments with  the  furnace  described  below,  he  succeeded  in 
obtaining  an  efficiency  of  33  per  cent.,  and  summed  up  his 
conclusions  as  follows  : — 

1.  The  degree  of  temperature  attainable  in  the  electric 
furnace  is  theoretically  unlimited. 

2.  Fusion  may  be  effected  in  a  perfectly   neutral   atmo- 
sphere. 

3.  Furnace  operations  can  be  carried  on  in  a  laboratory, 


FIG.  l. 

without  much  preparation,  and  under  the  eye  of  the 
operator. 

4.  The  limit  of  heat  practically  obtainable,  with  the  use  of 
ordinary  refractory  materials  is  very  high,  because,  in  the 
electric  furnace,  the  fusing  material  is  at  a  higher  tempera- 
ture than  the  crucible,  whereas,  in  ordinary  fusion,  the  tem- 
perature of  the  crucible  exceeds  that  of  the  material  fused 
within  it. 

The  historical  furnace  used  in  connexion  with  these  early 
experiments  is  depicted  in  Fig.  1,  and  consisted  of  a 


THEIR    INDUSTRIAL    APPLICATIONS 

refractory  crucible  A,  of  plumbago,  magnesia,  lime,  or  other 
suitable  material,  which  may  be  varied  according  to  the  nature 
of  the  substance  to  be  treated  within  it.  It  is  supported  at 
the  centre  of  a  cylindrical  jacket  B,  and  is  packed  around 
with  broken  charcoal,  which,  being  a  poor  conductor  of  heat, 
isolates  it  from  the  surrounding  atmosphere,  and  conserves 
the  heat  developed  within  the  crucible  to  such  an  extent 
that  there  is  very  little  loss  due  to  radiation  or  diffusion. 
The  negative  electrode  consists  of  a  massive  carbon  rod  C, 
passing  axially  through  the  centre  of  the  crucible  lid,  and 
free  to  move  vertically  therein,  the  clearance  opening  being, 
for  obvious  reasons,  very  small. 

The  cathode,  C,  is  suspended  from  the  lower  extremity  of 
a  copper  strap  D,  which  conducts  the  current  from  it,  being 
attached  at  its  upper  end  to  the  curved  extremity  of  a  hori- 
zontal beam  E.  The  positive  electrode  F,  which  may 
be  of  iron,  platinum  or  carbon,  consists  of  a  cylindrical  rod 
of  one  or  other  of  these  materials,  passing  up  through  the 
centre  of  the  crucible  base.  The  other  side  of  the  beam,  E, 
carries,  suspended  from  its  extremity  by  a  hinged  joint, 
a  hollow  soft  iron  cylinder  G,  forming  the  core  of  the  solenoid 
S.  The  core  G  works  in  a  dash-pot  P,  the  tendency  of 
the  solenoid  S,  when  active,  being  to  raise  it  against  the 
counteracting  force  of  the  adjustable  counterweight  W, 
thus  lowering  the  cathode  G  into  the  crucible.  The  solenoid 
winding  is  connected  in  shunt  to  the  two  electrodes. 

The  furnace^  was  originally  designed  by  Siemens  for  the 
fusion  of  refractory  metals,  and  their  ores  ;  consequently, 
once  the  action  is  started,  electrical  connexion  is  established 
between  the  lower  electrode  F  and  the  semi-metallic  mass 
in  the  crucible,  and  the  arc  continues  to  play  between  the 
surface  of  the  mass  and  the  movable  carbon  rod  C.  As 
the  current  through  the  furnace  increases,  that  through  the 
shunt  winding  of  the  solenoid  diminishes,  and  the  weight 
W,  coming  into  play,  causes  its  end  of  the  beam  to  descend, 
thus  raising  the  cathode  C,  and  restoring  equilibrium. 

3 


ELECTRIC    FURNACES    AND 

To  Moissan  we  are,  of  course,  indebted  for  much  valuable 
information  to  as  the  possibilities  opened  up  by  the  intro- 
duction of  the  electric  furnace,  and  the  results  of  his  researches 
into  the  subject,  duly  assembled  in  convenient  form  in  his 
book  Le  Four  Electrique,  are  well  worthy  of  careful  study 
by  those  interested  in  the  subject  of  high  temperatures. 

Moissan's  most  valuable  researches  into  the  chemistry 
of  high  temperatures,  rendered  possible  by  the  introduction 
of  the  electric  furnace,  were  carried  out  during  1893  and  1894. 
Many  conclusions  may  be  drawn  from  an  exhaustive  study 
of  Moissan's  work,  and  those  having,  or  promising  to  have 
an  industrial  importance  are  well  summarized  by  Blount,  in 
his  book  Practical  Electro-Chemistry •,  as  follows — 

"  The  stable  form  into  which  carbon,  whether  amorphous, 
or  crystallized  as  diamond,  tends  to  pass,  is  graphite.  Under 
ordinary  conditions,  carbon  does  not  melt,  but  passes 
directly  into  the  gaseous  state  ;  if  subjected  to  high  pressure, 
as  it  may  be  by  suddenly  cooling  a  liquid,  e.g.  iron,  in  which 
it  is  dissolved,  it  may  be  liquefied,  and  then  may  crystallize 
as  diamond. 

"  Lime,  magnesia,  molybdenum,  tungsten,  vanadium,  and 
zirconium  may  be  fused.  Silica,  zirconia,  lime,  aluminium, 
copper,  gold,  platinum,  iron,  uranium,  silicon,  boron  and 
carbon  may  be  volatilized.  The  oxides  among  these 
substances  may  be  deposited  in  a  crystalline  form.  Oxides 
usually  regarded  as  irreducible,  e.g.,  alumina,  silica,  baryta, 
strontia  and  lime,  uranium  oxide,  vanadium  oxide,  and 
zirconia  may  be  reduced  by  carbon  in  the  electric  furnace. 
Many  metals  which  are  reduced  with  difficulty  in  ordinary 
furnaces,  such  as  manganese,  chromium,  tungsten,  and 
molybdenum,  may  be  prepared  in  quantity.  Moreover, 
in  the  electric  furnace,  these  metals  may  be  obtained  of 
approximate  purity,  in  spite  of  their  great  tendency  to 
unite  with  the  oxygen  and  nitrogen  of  the  air.  It  often 
happens  that,  when  a  metallic  oxide  is  reduced  with  excess 
of  carbon  in  the  electric  furnace,  a  carbide  of  the  metal  is 

4 


THEIR   INDUSTRIAL   APPLICATIONS 

first  formed.     From  this  the  pure  metal  can  usually  be 
prepared  by  fusing  the  carbide  with  the  oxide  of  the  metal. 
The  carbon  is   oxidized  and  an  equivalent  of  the  metal 
reduced.     The    behaviour    of    such    metals    in   dissolving 
carbon  at  high  temperatures,  in  rejecting  it  on  cooling,  and 
in  losing  it  when  subjected  to  selective  oxidation,  in  general 
resembles  that  of  iron,  which  is  well  known.      One  class  of 
bodies    is    particularly    stable    at    the    high    temperatures 
attainable  by  the  electric  furnace — to  wit,  that  comprising 
the  carbides,  borides,  and  silicides.     These  substances  are 
usually  of  simple  composition  :    SiC  (silicon  carbide),   CaC2 
(calcium  carbide),    Mn3C  (manganese  carbide),  Fe2Si  (iron 
silicide),  FeB  (iron  boride),  CB6  (carbon  boride),  will  serve 
as  examples.     Some  members  of  the  group  are  extremely 
hard.     Thus  carbon  silicide  (or  silicon  carbide)  is  harder  than 
emery,    while    boron   carbide   and   titanium   carbide   may 
actually  serve  to  cut  a  diamond — not  merely  to  polish  it,  as 
does  silicon  carbide,  but  to  produce  definite  facets.     Others 
of  the  carbides  have  another  claim  to  interest  from  an  in- 
dustrial as  well  as  from  a  scientific  standpoint.     Everyone 
knows  nowadays  that  calcium  carbide  is  decomposed  by 
water  and  yields  acetylene  ;  but  it  is  not  always  realized  that 
the  property  of  thus  giving  rise  to  a  hydrocarbon  is  general 
for  a  large  number  of  similar  bodies,  e.g.  the  carbides  of 
lithium,  aluminium,  thorium,  and  cerium.      Lithium  carbide 
(Li2C2)   yields  acetylene  ;   aluminium  carbide   (A14C3)   gives 
methane  ;   cerium  carbide   (CeC2),   a   mixture  of  the  gases 
acetylene,  ethylene,  and  methane,  and  a  notable  proportion 
of  liquid  hydrocarbons.      This  brief  catalogue  of  facts  will 
show  how  large  a  field  for  industrial  research  exists,  and  how 
well  mapped  are  the  paths  by  which  it  may  be  entered." 

Passing  record  of  the  earlier  researches  into  the  possibilities 
of  the  electric  furnace  as  an  industrial  auxiliary  may  be 
gleaned  from  the  Report  of  the  Franklin  Institute,  July, 
1898,  on  the  researches  of  M.  Henri  Moissan. 

The  electric  furnace  utilized  by  Moissan  for  conducting 

5 


ELECTRIC   FURNACES   AND 

these  researches  was  devised  by  him,  and  is  of  very  simple 
construction.  It  belongs  to  that  class  known  as  "  Indirect 
arc  furnaces,"  so  called  from  the  fact  that  the  arc  itself  is 
not  brought  into  actual  contact  with  the  material  under 
treatment,  which  receives  its  heat,  instead,  by  reflection  from 
the  furnace  walls  or  roof.  It  is  represented  in  Fig.  2, 
and  consists  of  two  blocks  of  chalk,  A,  A,  so  hollowed  out 
that,  when  placed  together,  they  form  a  cavity  for  the 
reception  of  the  carbon  crucible  C,  which  contains  the 
material  to  be  treated,  and  constitutes,  in  point  of  fact,  the 
hearth  of  the  furnace.  Two  carbon  electrodes  E  E  pro- 
ject through  the  sides  of  the  blocks,  and  meet,  with  the 
exception  of  an  arcing  space,  at  a  point  just  above  the  mouth 


FIG.  2. 


FIG.  3. 


of  the  crucible  C.  Electrical  connexion  with  the  source  of 
current  is  secured  through  the  metal  clamps  M  M.  Metal 
bands  B  serve  to  hold  the  chalk  blocks  together  whilst  the 
furnace  is  active. 

As  a  laboratory  type,  this  simple  furnace  has  many 
advantages  ;  it  is  built  up  of  refractory  material,  and  com- 
prises comparatively  few  parts,  which  are  easily  taken  to 
pieces  and  reassembled.  Furthermore,  the  centre  of  activity, 
surrounded  as  it  is,  on  all  sides,  by  a  considerable  thickness 
of  refractory  and  non-conducting  material,  can  be  brought 
to  an  extremely  high  temperature,  with  very  little  accom- 
panying loss  of  energy. 

6 


THEIR  INDUSTRIAL  APPLICATIONS 

One  of  the  earliest  resistance  furnaces  or  muffles,  which 
depended  for  its  action  on  the  heat  generated  in  a  conductor 
of  reduced  cross-section  embedded  in  the  substance  of  its 
walls,  was  that  patented  by  Faure  in  1883.  It  was  intended 
for  the  manufacture  of  sodium,  and  a  sectional  view  is  repre- 
sented in  Fig.  3,  from  which  it  will  be  seen  that  the 
conductors  c  c  were  embedded  in  the  hearth.  One  or  two 
later  modifications  of  this  early  type  are  described  in  the 
section  dealing  with  laboratory  furnaces. 

The  commercial  resistance  furnace  is  the  outcome  of  the 
inventive  genius  of  Messrs.  Eugene  H.  and  Alfred  H. 
Cowles,  who,  after  numerous  experiments,  selected  coarsely 
powdered  carbon  as  a  suitable  material  for  the  resistance 
core,  whilst,  at  the  same  time,  a  necessary  ingredient,  for  the 
reduction  of  oxides. 

From  an  historical  point  of  view,  the  following  extract 
from  a  paper  read  before  the  American  Association  for 
the  Advancement  of  Science,  in  1885,  by  Professor  Chas. 
F.  Mabery,  may  prove  of  interest : 

"  A  short  time  since,  Eugene  H.  Cowles,  and  Alfred  H. 
Cowles,  of  Cleveland,  conceived  the  idea  of  obtaining  a  con- 
tinuous high  temperature,  on  an  extended  scale,  by  intro- 
ducing into  the  path  of  an  electric  current,  some  material 
that  would  afford  the  requisite  resistance,  thereby  pro- 
ducing a  corresponding  increase  in  the  temperature.  After 
numerous  experiments,  that  need  not  be  described  in  detail, 
coarsely  pulverised  carbon  was  selected  as  the  best  means 
for  maintaining  a  variable  resistance,  and  at  the  same  time 
the  most  available  substance  for  the  reduction  of  oxides. 
When  this  material,  mixed  with  the  oxide  to  be  reduced, 
was  made  a  part  of  the  electric  circuit  in  a  fire-clay  retort, 
and  submitted  to  the  action  of  a  current  from  a  powerful 
dynamo  machine,  not  only  was  the  reduction  accomplished, 
but  the  temperature  increased  to  such  an  extent  that  the 
whole  interior  of  the  retort  fused  completely.  In  other 

7 


ELECTRIC   FURNACES    AND 

experiments,  lumps  of  lime,  sand,  and  corundum  were  fused, 
with  indications  of  a  reduction  of  the  corresponding  metal ; 
on  cooling,  the  lime  formed  large,  well-defined  crystals, 
the  corundum,  beautiful  red,  green,  and  blue,  hexagonal 
crystals. 

"  Experiments  already  made  show  that  aluminium,  silicon, 
boron,  manganese,  magnesium,  sodium,  and  potassium  can 
be  reduced  from  their  oxides  with  ease.  In  fact  there  is  no 
oxide  that  can  withstand  temperatures  attainable  in  this 
electrical  furnace.  Charcoal  in  considerable  quantities  is 
changed  to  graphite ;  whether  this  indicates  fusion,  or 
solution  of  carbon  in  the  reduced  metal,  has  not  been  fully 
determined. 

"  As  to  what  can  be  accomplished  by  converting  enormous 
electrical  energy  into  heat  within  its  limited  space,  it  can  only 
be  said  that  it  opens  the  way  into  an  extensive  field  for 
pure  and  applied  chemistry.  It  is  not  difficult  to  conceive 
of  temperatures  limited  only  by  the  capability  of  carbon  to 
resist  fusion." 

The  Cowles  furnace  made  its  first  appearance  in  public 
in  1885,  its  initial  application  to  the  needs  of  industry  being 
in  the  reduction  of  oxides  (vide  the  zinc  furnace,  in  which  a 
graphite  crucible  forms  one  electrode). 

In  1887,  the  Cowles  Brothers  took  out  a  patent  on  a 
furnace  with  an  arrangement  for  continuous  feeding  of 
the  charge. 

Temperatures  Attainable  in  the  Electric  Furnace. — The 
maximum  temperature  attainable  by  the  combustion  of 
fuel,  either  in  solid,  liquid,  or  gaseous  form,  and  under  the 
most  favourable  conditions  for  the  conservation  of  the  heat 
developed,  is  in  the  neighbourhood  of  2,0000C.=3,632°F., 
although  Heraeus,  in  a  paper  before  the  German  Bunsen 
Society  in  1902,  claimed  that  he  had  succeeded  in  con- 
structing a  non-electric  furnace,  in  which  temperatures  up  to 
2,200  C.=3,992°F.  could  be  produced.  He  employs  an 

8 


THEIR  INDUSTRIAL  APPLICATIONS 

iridium  tube,  suitably  mounted  in  a  furnace,  and  heated  by 
means  of  an  oxy-hydrogen  flame.  The  temperature  was 
measured  by  the  aid  of  a  thermo-couple,  consisting  of  abso- 
lutely pure  iridium,  and  an  alloy  of  90  per  cent,  iridium  with 
10  per  cent,  ruthenium.  Up  to  1,650°C.=3,002°F.  a  direct 
comparison  was  made  between  this  thermo-couple,  and  a 
standard  calibrated  by  the  Reichsanstalt.  Above  this 
temperature  the  several  values  were  arrived  at  by  calcula- 
tion. 

The  temperature  of  the  electric  arc  itself  has  never  been  de- 
termined, the  only  available  data  on  the  subject  of  such  high 
temperatures  being  the  results  of  temperature  or  calori- 
metric  measurements,  made  on  the  active  extremities  of 
the  carbons.  Thus,  in  1893,  Violle  tested  the  temperature 
of  the  positive  carbon  crater  by  photometric  methods,  and 
found  it  to  be  3,500°C.=6,332°F.,  and  independent  of  the 
magnitude  of  the  current  producing  it,  between  10  and  400 
amperes.  This  estimate  is  only  subject  to  error  through  a 
corresponding  miscalculation  of  the  specific  heat  of  carbon, 
and  was  subsequently  modified  by  the  investigator  to 
3,600°C.:=6,5120F.,  as  the  result  of  assigning  a  slightly 
different  value  to  this  specific  heat. 

It  is  probable  that  the  temperature  of  the  arc  itself  is 
slightly  higher  than  the  above  figure,  which  may  nevertheless 
be  taken  as  the  approximate  limiting  temperature  of 
furnaces  operating  on  the  arc  principle,  at  atmospheric 
pressure,  and  with  carbon  electrodes.  Assuming  this  to  be 
the  temperature  at  which  carbon  vaporizes,  it  is  obvious  that 
a  limit  is  similarly  set  upon  the  temperature  obtainable  in 
furnaces  of  the  "  resistance  "  type,  in  which  a  carbon  core 
is  employed. 

Basing  his  deductions  upon  an  interesting  and  instructive 
experiment  performed  by  Moissan,  Townsend  (Electrical 
World,  April  6,  1901),  suggests  defining  the  limiting  tempera- 
ture of  the  arc  between  carbon  electrodes,  as  that  tempera- 
ture at  which  the  complex  carbon  molecule  breaks  down  ; 

9 


ELECTRIC  FURNACES   AND 

and  that  of  the  resistance  furnace,  with  carbon  core,  as  th6 
true  point  of  vaporization  of  carbon,  the  former  tempera- 
ture being  distinctly  lower  than  the  latter. 

The  experiment  referred  to  as  having  been  performed  by 
Moissan  is  mentioned  in  Comptes  Eendus,  vol.  cxix,  p.  776, 
and  consisted  in  exposing  to  the  direct  heat  of  a  2000  ampere, 
80  volt  arc,  a  carbon  tube  having  an  internal  diameter  or  bore, 
of  one  centimetre.  The  experiment  served  to  demonstrate 
the  volatilization  and  condensation  of  carbon,  the  interior 
of  the  tube  becoming  filled,  under  the  intense  heating  effect 
of  the  arc,  with  carbon  vapours,  which  subsequently  con- 
densed upon  its  walls  in  the  form  of  graphite.  Crystallized 
silicon,  placed  at  the  lower  extremity  of  the  tube,  fused  and 
volatilized,  with  the  result  that  its  ascending  vapour,  meet- 
ing the  descending  carbon  vapour,  combined  with  it  to  form 
transparent  needle-like  crystals  of  silicon  carbide  (carbor- 
undum). 

Townsend  argues  that,  since  silicon  carbide  was  formed  in 
this  manner  the  temperature  of  the  vapours  was  below  that  at 
which  this  compound  is  decomposed,  e.g.  below  that  of 
the  Acheson  graphite  furnace  ;  hence  his  deductions  as  to 
the  relative  limiting  temperatures  of  arc  and  resistance 
furnaces  as  set  forth  above. 

The  heat  intensity,  or  temperature  attainable,  in  an  electric 
furnace  depends,  among  other  things,  on  the  heat-conserving 
qualities  of  the  materials  of  which  the  furnace  is  constructed. 
In  furnaces  of  the  Moissan  type,  but  lined  with  blocks  of 
pure  carbon,  and  reinforced,  on  the  outside,  with  a  re- 
fractory non-conductor  of  heat,  such  as  chalk  or  magnesia, 
it  is  possible,  therefore,  to  obtain  a  temperature  of  approxi- 
mately 4,000°C.=7,232°P.  whilst  temperatures  ranging 
from  2,000°-3,500°C.=:3,6320-6,3320F.,are  easily  reached 
and  maintained  in  the  commercial  electric  furnace. 

Classification. — There  are  two  leading  types  of  electric 
furnace,  distinguished  from  one  another  by  the  method 
in  which  the  heat  energy  is  produced.  They  are  known 

10 


^ \  *  B 
X-    V   OF  THE 

{  UNIVERSITY   ) 

\^  <?4»  iroftH^^^ 

THEIR   INDUSTRIAL   APPLICATIONS 

respectively  as  "  Arc  "  and  "  Resistance  "  furnaces.  The 
former  performs  its  work  by  virtue  of  the  intense  heat 
generated  by  the  arc  set  up  between  two  or  more  electrodes, 
one  of  which  is  frequently  constituted  by  the  lining,  or 
base,  of  the  furnace  chamber  itself.  The  latter  derives 
its  heating  power  from  the  passage  of  a  heavy  current 
through  an  attenuated  conductor  of  high  resistance,  such 
as  a  carbon  pencil. 

These  two  main  classes  may  be  subjected  to  further 
subdivision,  depending  upon  the  principle  of  their  con- 
struction and  working.  The  arc  furnaces,  for  example, 
may  be  divided  into  those 
in  which  the  raw  material 
to  be  heated  is  subjected 
to  the  direct  heat  of  the  arc, 
and  is  brought  into  actual 
contact  with  it,  and  those 
in  which  the  heating  is 
effected  indirectly,  either  by 
conduction,  or  reflection  from 
the  roof  or  walls.  In  this 
latter  type,  to  which  belongs 
the  Moissan  furnace  already 
described,  the  charge  does 

not  come  into  contact  with  the  electrodes  at  all,  but  is 
situated  below  the  plane  of  the  arc,  and  sometimes  partially 
protected  from  it,  thus  reducing  the  chances  of  contamina- 
tion by  particles  which  might  become  detached  therefrom,  a 
very  necessary  precaution  in  some  processes,  such  as  glass 
manufacture,  for  example. 

Another  way  of  classifying  furnaces,  adopted  by  some 
writers,  is  according  to  their  construction,  and  the  arrange- 
ment of  the  electrodes.  Thus  arc  furnaces  may  be  sub- 
divided under  separate  headings,  according  to  whether 
the  electrodes  are  horizontal,  vertical,  or  parallel.  A 
typical  arc  furnace,  with  horizontal  electrodes,  is  shown 

II 


FIG.  4. 


ELECTRIC    FURNACES    AND 

in  diagram  in  Fig.  4,  E  E  being  the  electrodes,  and  H 
the  refractory  hearth,  or  crucible,  provided  with  a  tap- 
hole,  as  shown,  at  its  lowest  point,  for  drawing  off  the  molten 
products  of  the  reaction. 

Resistance  furnaces,  sometimes  called  "  Incandescent 
Furnaces,"  may  be  similarly  subdivided,  according  to 
whether  the  heating  is  directly  or  indirectly  effected  ;  a 
further  distinction  also  arises  out  of  the  nature  of  the 
resistance  itself  ;  in  some  cases,  this  is  independent,  and 
takes  the  form  of  a  carbon  pencil,  or  even  a  glower  of  the 
Nernst  type,  whilst  in  others  it  is  constituted  by  a 
poorly  conducting  column  of  the  unconverted  charge  it- 
self. 

Electrolytic  furnaces  are  essentially  of  the  resistance 
type,  the  resistance  in  this  case  being  the  electrolyte, 
usually  a  fused  salt,  under  treatment. 

Another  modern  development  of  the  resistance  furnace 
principle  is  that  class  of  apparatus  known  as  "  Induction 
Furnaces,"  of  which  the  Kjellin  furnace,  for  the  manu- 
facture of  steel,  is  a  typical  example,  and  will  be  described 
later  on.  These  induction  furnaces  depend  for  their 
action  upon  the  heating  effect  of  a  current  induced  in  them 
by  a  neighbouring  conductor  through  which  an  alternating 
current  is  flowing.  They  are,  in  effect,  transformer  fur- 
naces, the  furnace  itself,  or  rather  its  contents,  forming 
a  closed-circuit  secondary  winding,  in  which  is  induced 
a  heavy  current,  by  the  comparatively  small  current  flowing 
through  a  neighbouring  primary  winding  of  many  turns. 
The  principal  advantage  of  this  class  lies  in  the  complete 
absence  of  troublesome  electrodes  ;  no  minor  consideration, 
as  will  be  seen  when  dealing  with  the  various  electric  furnace 
processes. 

There  is  yet  another  type,  which  is,  however,  confined, 
for  the  greatei  part,  to  small  units  and  laboratory  apparatus, 
and  is  known  as  the  "  Tube  Furnace."  A  cylindrical  or 
tubular  construction  offers  several  advantages,  more 

12 


THEIR    INDUSTRIAL    APPLICATIONS 

especially  for  laboratory  work  and  experimental  research. 
Tube  furnaces  operate  either  on  the  resistance  principle, 
or  a  combination  of  both  arc  and  resistance  heating,  and 
are  dealt  with  in  a  special  section. 

Two  qualifying  terms  often  used  in  connexion  with 
electric  furnace  work  are  "  Intermittent "  and  "  Con- 
tinuous." An  intermittent  furnace  is  one  in  which  only 
one  charge,  equal  to  the  capacity  of  the  furnace,  can  be 
dealt  with  at  a  time,  without  interrupting  the  operation 
for  the  purpose  of  removing  the  product.  A  continuous 
furnace,  on  the  other  hand,  is  so  constructed  with  regard 
to  its  tapping  and  feed  arrangements,  that  a  process  can 
be  carried  on  continuously  without  shutting  down,  the 
material  under  treatment  either  passing  through  at  a 
regular  rate,  or  the  furnace  being  partially  relieved  of  its 
contents  at  regular  intervals  without  necessitating  a  stop- 
page of  the  current.  Continuous  furnaces  are  sometimes 
referred  to  as  "  Tapping  "  furnaces. 

As  regards  the  relative  advantages  and  disadvantages 
of  the  arc  and  resistance  principles  of  electric  furnace 
working,  it  may  be  stated  in  general  that  the  intense  and 
more  or  less  concentrated  heat  developed  in  the  arc  is 
unsuitable  for  many  commercial  processes,  which  call  for 
a  less  violent  and  more  readily  controllable  source  of  heat, 
such  as  is  provided  in  the  resistance  principle  of  con- 
struction. 

Here,  again,  we  are  confronted  with  further  difficulties, 
for,  if  the  resistance  core  be  composed  of  the  material 
itself  under  treatment,  such,  for  example,  as  a  mixture  of 
ore  and  slag,  in  an  electric  smelting  furnace,  the  current, 
and  therefore  the  heating  effect,  will  be  subject  to  extreme 
variations,  depending  upon  the  changes  brought  about 
in  the  conductivity  of  the  core  as  the  operation  proceeds, 
and  the  liberated  metal  asserts  its  presence.  To  mitigate 
this  drawback  to  a  certain  extent,  the  molten  product 
must  be  continually  tapped  off,  such  that  a  constant  cross- 

13 


ELECTRIC    FURNACES    AND 

sectional  area  of  resistance  core  may  be,  as  far  as  possible, 
maintained. 

Better  conditions  for  the  control  and  regulation  of  the 
temperature  obtain  in  resistance  furnaces  with  independent 
cores,  i.e.  furnaces  in  which  the  resistance  column  does 
not  form  part  and  parcel  of  the  charge  under  treatment, 
but  is  independent  of  it,  and  maintains  its  shape  and  cross- 
section,  within  reasonable  limits,  throughout  the  process. 
The  main  drawback  to  their  use  is,  of  course,  the  extra 
expense  involved  by  the  introduction  of  such  a  core,  and 
its  subsequent  periodical  renewal. 

Rasch  (Zeit.  /.  Elektrochemie,  February  19,  1903)  deprecates 
the  use  of  the  arc  furnace,  with  carbon  electrodes,  for  the 
majority  of  processes.  He  cites  the  following  requirements 
as  essential  to  the  success  of  pyrochemical  reactions  in 
general — 

"  The  electrodes  must  be  capable  of  withstanding  a  high 
energy  density,  and  a  high  temperature  ;  they  must  not 
be  oxidized,  and  must  not  exercise  a  reducing  action  on 
the  reaction  to  be  obtained." 

He  suggests  the  substitution  of  conductors  of  the  second 
class  for  carbon  ;  e.g.,  rods,  or  tubes,  of  magnesia,  aluminium 
oxide,  etc.,  which  require  to  be  pre-heated,  after  the  manner 
of  a  Nernst  lamp  glower,  before  they  become  conductors. 
This  principle  has  already  been  applied  to  laboratory  fur- 
naces, and  small  units,  but  its  adoption  on  a  more  extensive 
scale  is  at  present  limited  by  the  cost  of  the  material,  and 
the  difficulties  incidental  to  the  construction  of  a  tube 
furnace  of  any  magnitude. 

General  Remarks. — Employed  for  heating  purposes, 
electricity  is  only  capable  of  evolving  that  quantity  of 
thermal  energy  represented  by  Joule's  equivalent  of  the 
energy  originally  consumed  in  generating  the  current. 
In  the  case  of  a  steam-driven  plant,  the  'heat  energy  avail- 
able at  the  furnace  terminals  is  only  a  small  fraction  (from 
yo  to  sV)  of  the  calorific  value  of  the  coal  used  in  the  boiler 

14 


THEIR    INDUSTRIAL    APPLICATIONS 

furnaces.  Of  this  latter  about  one-fifth  is  lost  in  the  flues 
during  combustion  :  the  waste  gases  account  for  a  con- 
siderable proportion,  of  far  greater  value,  from  a  heating 
point  of  view,  than  the  electricity  generated  ;  whilst  some 
75  per  cent,  of  fuel  energy  is  present  in  the  exhaust  steam. 
It  will  readily  be  seen,  therefore,  that  electric  heat, 
derived  from  steam-driven  plant,  is  only  commercially 
applicable  in  special  cases,  involving  especially  high  tem- 
peratures, which  are  unattainable  by  ordinary  combustion 
methods,  concentrated  heating  effect,  or  where  the  value 
of  the  substances  under  treatment,  and  the  necessity  for 
maintaining  them  in  a  pure  state,  outweigh  the  cost  of  the 
heating  itself,  and  render  it  a  secondary  consideration. 

With  natural  water  power,  however,  the  matter  assumes 
a  different  aspect.  Here  we  have  a  frequently  unlimited 
supply  of  energy,  which  is  only  costing  the  interest  on 
capital  outlay  for  plant  and  maintenance,  so  that  the  com- 
paratively wasteful  transformation  of  water  power  into 
thermal  energy  becomes  a  minor  consideration. 

In  nearly  all  electro-chemical  and  electro-metallurgical 
processes,  the  cost  of  the  electrical  energy  constitutes  a 
considerable  percentage  of  the  total  cost  of  operation ; 
usually  25  per  cent,  or  more,  sometimes  as  much  as  90  per 
cent.  Cheap  electrical  energy  is  therefore  an  essential 
requirement  for  the  economical  working  of  an  electric 
furnace  process. 

The  principal  advantages  of  the  electric  furnace,  from 
an  industrial  standpoint,  may  be  summarized  as  follows  : — 

1.  The  time  required  for  a  reaction  is  reduced,  and  the 
yield  increased  for  a  given  time. 

2.  Reactions  take  place  more  completely. 

3.  The  heating  effect  is  concentrated  at  the  point  where 
it  is  most  required. 

4.  It   is    capable    of   bringing   about    high    temperature 
reactions  impossible   at  ordinary  temperatures. 

5.  Operations  may  be  readily  conducted  in  the  presence 


ELECTRIC    FURNACES    AND 

of  various  gases,  bringing  their  chemical  action  into  play 
on  other  substances  at  high  temperatures,  or  causing  one 
or  more  gases  to  react  together. 

In  laying  out  an  electric  furnace  plant,  it  is  essential 
that  the  furnaces  be  as  near  to  the  source  of  current  as  is 
compatible  with  the  safety  of  the  generators,  and  accessi- 
bility of  the  former.  No  undue  loss  of  energy  is  then 
likely  to  take  place  in  the  main  connecting  cables,  whilst 
the  quantity  of  copper  required  for  the  latter  is  reduced 
to  a  minimum.  Some  appreciable  separation  between 
the  two  is,  of  course,  essential,  owing  to  the  intense  heat 
which  prevails  in  the  immediate  neighbourhood  of  the 
furnace,  and  which  would  prove  prejudicial  to  the  dynamos. 
M.  Keller  advocates  a  separation  of  two  metres,  with  a 
dividing  wall  between  generator  and  furnace.  The  cables 
would  then  be  from  18  to  20  metres  long,  and  the  power 
factor  as  high  as  0'9. 

For  electric  furnace  work,  in  the  absence  of  electrolytic 
action,  an  alternating  current  is  more  easily  regulable, 
and  yields  better  heating  effect  than  a  direct  current. 

According  to  Mr.  J.  B.  C.  Kershaw  (Electrical  Review, 
July  7,  1899),  the  first  instance  of  three-phase  currents 
being  commercially  employed  in  electric  furnace  work  was 
in  the  manufacture  of  calcium  carbide,  at  Langenthal,  in 
Switzerland.  The  furnaces  are  of  the  movable  hearth 
type,  and  three  are  worked  simultaneously,  each  taking 
current  of  one  phase,  viz.  1,000  to  1,500  amperes  at  75 
volts. 

The  repulsion  exerted  by  a  strong  magnetic  field  upon 
the  electric  arc  has  not  been  without  its  attractions  for 
the  furnace  inventor,  as  instance  a  patent  granted  in  1897 
to  W.  H.  Monk.  The  principle  of  the  invention  is  equally 
applicable  to  either  arc  or  resistance  furnaces,  and  consists 
in  the  provision  of  a  rotating  magnetic  field  in  the  neigh- 
bourhood of  the  arc  or  heating  current,  whereby  the  latter 
is  also  caused  to  rotate  or  circulate  through  the  mass  of 

16 


THEIR    INDUSTRIAL    APPLICATIONS 

the  material  to  be  heated,  and  thereby  extend  its  sphere 
of  influence. 

In  one  form  of  arc  furnace  on  this  principle,  detailed 
in  the  published  specification,  arcs  were  set  up  between 
concentric  tubular  carbons,  which  also  served  as  feed 
passages,  and  a  solid  electrode,  mounted  on  an  iron  plate. 
Surrounding  this  was  an  iron  ring,  suitably  protected  from 
the  intense  heat,  and  wound  continuously,  with  four  branch 
connexions,  whereby  it  could  be  supplied  with  two  alternat- 
ing currents  in  quadrature,  to  produce  the  rotating  field. 

A  rotating  field  is  similarly  produced  around  the  central 
resistance  core  or  cores  in  a  furnace  working  on  the  latter 
principle: 

The  project  is  an  ingenious  one,  and  worthy  of  mention, 
but  it  is  questionable  whether  the  extra  expense  involved 
in  the  furnace  construction,  to  say  nothing  of  the  power 
consumed  in  producing  the  required  magnetic  field,  is 
overset  by  the  attendant  advantages.  At  all  events,  there 
is  no  record  of  the  principle  having  been  adopted  in  practice.  \ 

Another  inventor,  I.  L.  Roberts,  adopts  the  travelling 
belt,  or  conveyor  principle,  with  a  view  to  securing  con- 
tinuity of  furnace  action.  His  invention  relates  to  a 
delivery  hopper,  and  flue,  or  casing,  covering  a  slowly 
travelling  belt,  woven  from  asbestos  coated  wire,  on  which 
the  raw  material  to  be  treated  is  deposited  from  the  hopper, 
and  carried  into  the  heat  zone  created  by  the  arc  set  up 
between  two  carbon  electrodes,  held  in  adjustable  clamps 
and  projecting  through  the  walls  of  the  flue. 

In  1898,  Messrs.  Siemens  Bros.  &  Co.  took  out  a  patent 
solely  on  a  form  of  furnace  construction  which  prevented 
the  ingress  or  egress  of  atmospheric  air  either  to  or  from 
the  interior  of  the  furnace.  To  this  end  the  raw  material 
under  treatment  was  built  up  in  the  form  of  a  thick  layer, 
capable  of  preventing  the  permeation  of  air,  whilst  the 
upper  carbon  electrode  was  given  a  tubular  form  and 
utilized  for  the  secondary  purpose  of  carrying  off  the  gases 

17  c 


ELECTRIC    FURNACES    AND 

produced  in  the  reaction,  without  permitting  combustion. 
This  tubular  construction  for  the  upper  electrode  has  since 
been  applied  in  many  different  designs  of  furnace,  and  is 
used,  not  only  as  a  flue  for  the  gases,  but  also  as  a  feed 
channel  for  the  raw  materials  to  be  treated. 

Statistics. — In  the  words  of  an  old  saw,  "  The  proof  of 
the  pudding  is  in  the  eating,"  and,  despite  the  somewhat 
wasteful  transformation  of  energy  entailed  by  the  industrial 
application  of  the  electric  furnace,  a  few  statistics  from 
various  sources  will  serve  to  show  that  in  many  cases,  and 
for  various  processes,  the  advantages  of  the  electric  furnace 
have  so  far  outweighed  this  drawback  as  to  warrant  their 
installation  on  a  scale  of  considerable  magnitude. 

According  to  Prof.  Borchers,  the  aggregate  power  utilized 
in  electro-chemical  and  electro-metallurgical  industries 
employing  electric  furnaces  in  1900  was — 

For  Calcium  carbide  manufacture      .          .      180,000  h.p. 
„    Aluminium  „  .          *        27,000     „ 

„    Carborundum  .          2,600     ., 


Total 209,600  h.p. 

The  total  output  of  electrical  power  at  Niagara  in  1901 
was  50,000  H.P.,  of  which  23,000  H.P.  was  consumed  in 
electro-chemical  and  electro-metallurgical  processes.  Among 
the  principal  consumers  for  electric  furnace  operations  are 
the  following,  the  statistics  being  taken  from  Cassier's 
Magazine  for  May,  1901 — 

The  Acheson  International  Graphite  Company — 1,000 
H.P.,  utilized  in  the  conversion  of  anthracite  into  graphite, 
at  a  pressure  of  80  volts. 

The  Pittsburg  Reduction  Company — 5,000  H.P.,  utilized 
in  the  extraction  of  aluminium  from  bauxite  by  the  Hall 
process.  Direct  current  at  160  volts. 

The  Carborundum  Company — 2,000  H.P.,  utilized  in 
the  manufacture  of  silicon  carbide.  Alternating  current  at 
J 10  volts. 

18 


THEIR    INDUSTRIAL    APPLICATIONS 

The  Niagara  Electro-Chemical  Company — 500  H.P., 
utilized  in  the  production  of  sodium,  and  sodium  peroxide 
from  caustic  soda  by  the  Castner  process ;  165  volts,  con- 
tinuous current. 

The  Union  Carbide  Company— 10,000  H.P.,  utilized  in 
the  manufacture  of  calcium  carbide.  Each  furnace  200  H.P. 
Alternating  current  at  110  volts  and  25  alternations  per 
secor'I. 

French  statistics  (1904)  show  that  out  of  a  total  of 
238,703  H.P.,  available  from  the  falls  of  the  Alps,  22,536  H.P. 
is  employed  in  the  manufacture  of  aluminium  ;  20,485  H.P. 
in  other  metallurgical  industries ;  and  104,466  H.P.  in 
calcium  carbide  manufacture. 

Scientific  Deductions. — The  principle  of  the  electrical 
furnace,  and  the  reactions  brought  about  by  the  extremely 
high  temperatures  produced  within  it,  have  been  advanced 
in  explanation  of  many  geological  facts,  hitherto  unex- 
plained, e.g.,  the  formation  of  natural  gases,  petroleum, 
bitumen,  graphite,  corundum,  etc.,  all  of  which  occur  in 
nature,  and  can  be  artificially  produced,  under  similar 
conditions,  by  the  direct,  or  indirect  aid  of  the  electric 
furnace. 

In  a  paper  before  the  French  Academie  des  Sciences 
(Comptes  Rendus,  134,  pp.  1185-1188),  MM.  Sabatier  and 
Sendereus,  writing  on  the  synthetic  production  of  petroleum, 
incidentally  call  attention  to  the  existence  of  the  carbides 
of  the  alkaline  earth  metals  in  nature.  In  addition  to 
opening  up  possibilities  of  artificial  petroleum  becoming 
an  electric  furnace  product,  this  fact  also  lends  colour  to  the 
oft-suggested  theory  that  processes  analogous  to  those  of 
the  high  temperature  reactions  brought  about  in  the  electric 
furnace  also  take  place  as  the  result  of  natural  phenomena. 

Moissan's  original  theory  of  the  natural  formation  of 
petroleum,  which  is  supported  by  the  results  obtained  by 
the  above  investigators,  is  that  it  results  from  the  action 
of  water  upon  natural  carbides,  under  certain  conditions 

19 


ELECTRIC    FURNACES    AND 

involving  the  presence  of  metals,  and  a  temperature  not 
exceeding  1490C=300°F. 

The  above  authorities  summarize  their  results  as  follows. 
A  liquid,  resembling  Caucasian  petroleum,  in  all  its  physical 
properties  is  obtained  by  passing  a  mixture  of  acetylene 
gas  and  hydrogen,  in  certain  proportions,  over  finely  divided 
nickel,  or  a  metal  belonging  to  the  same  chemical  group, 
maintained  at  a  temperature  of  from  200°-300°C  =  392°- 
572°F. 

Variations  in  the  physical  conditions  of  the  experiment 
resulted  in  the  formation  of  an  oil  resembling  Galician 
petroleum,  and,  like  it,  containing  aromatic  hydrocarbons, 
whilst  lowering  the  temperature  to  180°C=356°F.  furnished 
a  liquid  resembling  American  petroleum. 

The  passage  of  acetylene  gas  per  se  over  the  finely  divided 
metals  resulted  in  the  formation,  by  exothermic  reactions, 
of  hydrocarbons  of  the  unsaturated  series,  which,  when 
mixed  with  hydrogen,  and  again  passed  over  the  heated 
metal,  led  to  the  formation  of  a  similar  product  to  the  first, 
resembling  Caucasian  oil. 


20 


THEIR    INDUSTRIAL    APPLICATIONS 


SECTION  II 

ARC  FURNACES. 

An  indirect  arc  furnace,  for  the  treatment  of  metallic 
oxides  and  metalloids,  such  as  silica,  ferrous  chroma te, 
bauxite,  etc.,  and  converting  them  into  a  vitreous  and 
homogeneous  product  of  commercial  value,  is  repre- 
sented in  Fig.  5.  The  process  in  its  entirety  consists  in 
subjecting  the  raw  materials  to  the  radiated  or  luminous 
heat  of  an  arc,  which  fuses  them,  and  then  subsequently 
cooling  the  resultant  fused  mass.  The  furnace  in  which 
the  fusion  is  effected  is  of  simple  construction,  its  design 
being  such  that  the  charge  never  comes  in  actual  contact 
with  the  arc,  but  is  heated  solely  by  radiation  and  reflection. 
The  materials  to  be  treated  are  fed  in  through  a  central 
chimney  or  flue  F,  fitted  with  a  gas-tight  valve  V,  and  a 
connexion,  C,  for  producing  a  vacuum  in  the  furnace  chamber. 
On  reaching  the  bottom  of  F,  the  charge  divides  between 
the  two  inclined  chutes  BB,  which  form  a  bridge  or  dome 
immediately  over  the  arc  A.  In  passing  down  these,  it 
receives  a  preliminary  heating,  the  fusion  being  completed 
when  it  reaches  the  hearth,  H,  of  the  chamber,  by  the  direct 
radiant  heat  from  A. 

An  indirect  arc  furnace  devised  by  G.  de  Chalmont 
comprises  a  refractory  crucible,  supported  on  one  carbon 
electrode,  which  passes  vertically  up  through  the  base  of 
the  furnace  chamber,  whilst  the  remaining  electrode  is 
horizontally  disposed,  in  the  shape  of  four  radial  sections 
which  bear  on  the  outer  surface  of  the  wall  of  the  crucible. 
The  charge  is  thus  screened  from  the  direct  heat  of  the  arcs, 
which  play  over  the  exterior  of  the  crucible. 

21 


ELECTRIC   FURNACES    AND 

The  de  Chalmont  furnace,  invented  by  the  late  Dr.  de 
Chalmont,  and  employed  by  him  in  his  researches  on  metallic 
silicides,  presents  several  novel  and  interesting  features  in 
furnace  construction.  It  is  represented  in  diagrammatic 


FIG.  5. 


FIG.  6. 


section  by  Fig.  6,  and  consists  of  a  cast-iron  trough,  T, 
made  in  two  sections,  upper  and  lower  respectively,  which 
are  connected  by  a  flanged  joint  at  F.  The  whole  is  mounted 
on  wheels,  W,  for  portability.  A  carbon  lining,  C,  constitutes 
one  electrode  and  also  the  hearth  of  the  furnace  proper, 
which  is  provided  with  the  usual  tapping  hole  t,  and  flue  /. 
J  is  a  layer  of  refractory  insulating  material,  supporting  the 
lid  L,  which,  as  represented  in  the  figure,  is  given  a  sec- 
tional construction,  each  separate  portion  being  furnished 
with  a  distinct  conduit  for  water-cooling  purposes.  The 
upper  adjustable  electrode  A,  also  of  carbon,  enters  through 
a  stuffing  box  B,  in  the  centre  of  the  cover,  which  effectually 
prevents  ingress  of  air,  whilst  at  the  same  time  permitting 
the  necessary  adjustments  of  the  movable  electrode.  Sh 
is  a  shunt  interposed  between  the  upper  electrode  and  the 
cover  itself,  its  object  being  to  prevent  accidental  arcing 

22 


THEIR    INDUSTRIAL  APPLICATIONS 

between   them,   by   maintaining   them   both   at   the   same 
potential,  thus  protecting  the  lid  from  injury. 

The  Denbergh  arc  furnace,  invented  by  Dr.  F.  P.  van 
Denbergh,  is  specially  adapted  to  a  variety  of  operations, 
chief  among  which  may  be  cited  the  manufacture  of  sul- 
phuric and  phosphoric  acids,  and  alkaline  silicates,  such  as 
"  water-glass."  The  furnace  is  represented  in  sectional 
elevation  in  Fig.  7.  It  comprises  a  fire-brick  structure  F, 
contracted  below,  as  shown,  to  form  a  crucible  for  the 
reception  of  the  molten  pro- 
ducts. The  upper  chamber 
where  the  actual  fusion  takes 
place  is  lined  interiorly  with 
a  refractory  layer  R,  which 
remains  unaffected  by  the 
gases  and  vapours  produced. 
E  E  are  carbon  electrodes, 
each  mounted  in  a  species  of 
universal  ball  joint,  built 
into  the  furnace  wall,  which 
permits  a  longitudinal  or  feed 
adjustment,  and,  at  the  same 
time,  a  swivelling  motion  of 
the  electrodes,  whereby  the 

position  of  the  arc  may  be  regulated  at  will.  The  base  B  is 
removably  rabbited  into  the  furnace  walls,  and  supported 
in  position  by  the  loose  bricks  6,  b.  A  flue,  the  opening  to 
which  is  shown  at  o,  leads  up  from  the  base  of  the  furnace 
within  the  walls  to  a  point  which  determines  the  level  of 
the  molten  mass  within  ;  its  position,  within  the  heated 
walls,  effectually  prevents  "  freezing "  and  consequent 
stoppage  of  the  outlet.  A  is  an  outlet  at  the  top  of  the 
furnace,  for  gaseous  products.  The  raw  material  is  fed 
in  at  a  regular  rate,  from  the  hopper  H,  by  a  reciprocating  y 
piston-feed  mechanism  P,  driven  by  the  belt  D,  and  falls 
vertically  through  the  central  heat  zone  of  the  arc. 

23 


ELECTRIC   FURNACES   AND 

In  this  furnace,  the  inventor  manufactures  phosphoric 
acid  from  apatite,  etc.  The  mineral  is  first  crushed,  and  a 
quantity  of  sand  added  to  it  to  serve  as  a  flux.  Under  the 
heat  of  the  arc,  phosphorus  is  liberated  from  the  mixture. 
The  atmosphere  of  the  furnace  is  rich  in  oxygen,  with 
which  the  phosphorus  immediately  enters  into  combination, 
forming  oxides.  These  latter  are  subsequently  hydrated 
by  steam,  which  is  introduced  into  the  furnace  chamber  for 
the  purpose. 

A  somewhat  ingenious  continuous  arc  furnace  is  the 
invention  of  Mr.  F.  J.  Patten.  The  principal  mechanical 
and  electrical  features  of  its  construction  are  represented 


FIG.  8. 

in  Fig.  8.  It  consists,  in  the  main,  of  a  vertical  centre 
spindle  S,  suitably  supported  for  free  rotation,  in  bearings, 
and  carrying  a  flat  annular  table  T,  which,  protected  by  a 
refractory  bed  B,  constitutes  the  moving  hearth  or  floor 
of  the  furnace,  upon  which  is  spread  the  raw  material  to  be 
subjected  to  the  action  of  the  arc.  The  revolving  table  is 
additionally  supported  on  ball  bearings  b  b.  The  two  carbon 
electrodes  E  E  are  carried  by  vertical  supports,  capable 
of  lateral  adjustment  by  means  of  a  screw  carriage,  mounted 
on  a  radial  arm,  which  also  permits  of  their  rotation  inde- 
pendently of  the  hearth.  A  greater  number  of  electrode 
carriers  may  be  added,  if  it  be  wished  to  increase  the 
capacity  of  the  furnace. 

An  additional   feature   in   the   construction   consists   of 

24 


THEIR    INDUSTRIAL    APPLICATIONS 

electro-magnets  m  m  attached  to  the  electrode  terminals, 
which,  when  active,  deflect  the  arcs  down  on  to  the  charge 
after  the  manner  of  a  blow-pipe. 

A  patent,  dated  July  17,  1897,  granted  to  C.  Bertolus, 
covers  the  application  of  polyphase  currents  to  electric 
furnace  working  on  the  arc  principle. 

The  advantages  of  three-phase  currents  for  electric 
furnaces  of  the  arc  type  are — 

1.  More    uniform    distribution   of   heat   throughout   the 
mass  of  material  under  treatment. 

2.  Accidental  extinction  of  the  arc  a  very  remote  con- 
tingency. 

3.  Polyphase  generators  are  of  simpler  construction,  and 
less   liable    to    breakdown,    consequent   upon   the   sudden 
variations  in  load,  incidental  to  arc  furnace  working. 

Koller's  arc  furnace  construction  is  very  simple,  and  was 
devised  with  a  view  to  securing  better  distribution  of  the 
heating  effect  throughout  the  charge,  whilst  at  the  same 
time  rendering  the  furnace  suitable  for  use  on  circuits  of 
higher  voltage  than  usual.  It  consists  of  a  longitudinal 
chamber,  with  massive  carbon  blocks,  projecting  through 
the  end  walls.  A  series  of  carbon  blocks,  supported  in  line 
with  these  terminal  electrodes,  are  arranged  along  the 
furnace  chamber  at  regular  intervals,  their  number  varying 
according  to  the  voltage.  The  arc  is  thus  split  up  into  a 
series,  and  a  number  of  heated  regions  are  secured  in  the 
centre  of  the  mass  of  raw  material,  which  is  packed  around 
the  blocks. 

A  rather  ingenious  application  of  the  arc  furnace  principle 
to  the  carbonizing  of  electric  lamp  filaments  is  the  outcome 
of  a  patent  granted  to  W.  L.  Voelker,  the  inventor  of  the 
Voelker  Carbide  Lamp.  The  device  consists  of  a  fire- 
proof crucible,  enclosing  the  arcing  space  between  two 
vertical  carbon  electrodes,  which  constitute  the  terminals 
of  the  furnace.  The  untreated  filament  is  reeled  off  from 
a  drum,  through  orifices  in  the  walls  of  the  crucible,  on  to 

25 


ELECTRIC   FURNACES    AND 

another  receiving  drum,  its  line  of  passage  through  the 
crucible  being  so  disposed  as  not  to  pass  through  the  axis 
of  the  arc  itself,  but  to  one  side  of  it,  the  arc  being  deflected 
on  to  it.  The  crucible  is  kept  charged,  either  with  carbon 
vapour,  or  a  hydrocarbon  reducing  gas,  during  the  treatment. 
A  patent  for  a  similar  method  of  procedure  in  the  manu- 
facture of  filaments  for  incandescent  lamps,  has  been  granted 
to  R.  A.  Nielsen,  and  is  applicable  to  oxides  of  the  rare 
earths,  such  as  are  utilized  in  Nernst  lamp  glowers.  These 
oxides  are  subjected  to  the  heat  of  the  arc,  whilst  shielded 
from  its  electrolytic  action  by  a  tube  of  refractory  material, 
until  they  melt  or  soften,  whereupon  they  are  drawn  out 
into  threads  of  the  required  diameter. 

Action  of  the  Arc  Furnace. — A  paper  by  MM.  Gin  and 
Leleux,  before  the  Paris  Academy  of  Science  in  1898,  dis- 
cussed the  action  of  the  electric  arc  furnace,  from  a  theo- 
retical standpoint,  as  compared  with  the  results  obtained 
in  actual  practice.  We  may  regard  the  fall  of  potential 
between  the  electrodes  of  an  arc  furnace  as  taking  place 
through  the  resistance  column  of  gas  which  lies  between  them, 
and  is  the  product  of  the  volatilization  of  either  the  elec- 
trodes themselves,  or  a  portion  of  the  raw  material  under 
treatment.  Regarding  this  column  of  gas  as  a  theoretically 
perfect  cylinder,  having  a  sectional  area  equal  to  that  of 
the  electrodes,  and  surrounded  by  a  perfect  heat-conserving 
screen  or  jacket,  we  can  prove  that  the  temperature  would 
increase  in  direct  proportion  to  the  square  of  the  current 
density,  and  the  ratio  of  the  resistivity  to  the  specific  heat 
per  unit  volume,  of  the  atmosphere  of  the  arc. 

In  actual  practice,  however,  this  result  is  never  obtained  ; 
the  arc  forms  a  species  of  pocket  or  envelope,  with  a  small 
orifice  in  its  upper  portion,  through  which  the  various  gases, 
resulting  from  the  reaction,  make  their  escape.  The  size 
of  this  envelope,  or  cavity,  increases,  until  a  point  is  reached, 
at  which  the  resultant  heat  of  the  arc  is  equivalent  to  the 
heat  dissipated  in  the  surrounding  raw  material. 

26 


THEIR    INDUSTRIAL    APPLICATIONS 


SECTION   III 

RESISTANCE  FURNACES  AND  TYPICAL  PROCESSES 

The  heat  developed  in  a  conductor,  such  as  the  core  of  a 
resistance  furnace,  by  the  passage  of  an  electric  current 
through  it,  depends  upon — 

1.  The  ohmic  resistance  of  the  conductor. 

2.  The  magnitude  of  the  current. 

3.  The  duration  of  its  flow. 

All  three  quantities  are  open  to  regulation  in  the  majority 
of  resistance  furnaces,  hence  the  facility  with  which  this 
type  lends  itself  to  exact  temperature  regulation  and  control. 

The  temperature  of  a  heating  resistance  core  depends 
upon  the  rate  of  development  of  heat  within  it,  and  upon 
the  rate  at  which  it  is  capable  of  dissipating  that  heat  by 
radiation  and  conduction.  The  ultimate  fixed  temperature 
of  a  resistance  furnace  core  is  attained  when  the  above  two 
quantities  are  exactly  equal,  i.e.  when  the  rate  at  which 
heat  is  dissipated  or  given  off  by  the  conductor  is  equal  to 
the  rate  at  which  it  is  developed. 

The  limit  of  temperature  attainable  in  such  a  conducting 
core  depends,  of  course,  upon  the  fusing  point  of  the  material 
of  which  it  is  composed. 

An  excellent  example  of  the  various  possibilities  of  a 
suitably  designed  resistance  furnace,  in  which  the  tempera- 
ture regulation  is  well  under  control,  and  can  be  altered 
with  a  fair  degree  of  accuracy  over  an  extended  range,  is 
to  be  seen  in  the  various  Acheson  furnace  processes,  in  which 

27 


ELECTRIC    FURNACES    AND 

silicon   and   carbon    constitute    the    raw    materials    under 
treatment. 

By  certain  variations  in  the  conditions  and  temperatures 
at  which  the  reactions  are  brought  about,  it  is  possible  to 
produce  carborundum,  "  white  stuff,"  silicon,  siloxicon,  or 
graphite,  at  will. 

With  resistance  furnaces  generally,  and  those  of  the 
Acheson  type,  with  only  a  partially  independent  core,  in 
particular,  the  question  of  efficient  temperature  regulation 
is  an  important  one,  in  that  it  cannot  be  effected  by  any 
change  in  the  internal  conditions  of  the  furnace  charge,  or 
core  ;  the  latter,  once  the  operation  is  started,  is  unalter- 
able, and  it  is  only  by  external  means  that  the  current, 
and  consequently  the  temperature,  can  be  governed  and 
regulated. 

A  feature  peculiar  to  this  type  of  furnace  is  a  high  internal 
resistance,  which  gradually  falls  during  working,  until, 
at  the  end  of  an  operation,  it  is  fairly  low,  a  condition  of 
things  which  can  only  be  compensated  by  corresponding 
regulation  of  the  voltage  at  the  furnace  terminals. 

The  actual  resistance  which  a  furnace  is  desired  to  have, 
can  only  be  procured,  or  reproduced,  by  experiment,  a 
process  in  which  the  choice  of  many  different  grades  of  core 
carbon,  together  with  a  variation  in  the  size  and  shape  of  the 
constituent  particles,  provides  a  wide  field  for  initial 
adjustment. 

Herr  Otto  Vogel,  a  German  authority,  has  made  the 
following  suggestions  with  regard  to  resistance  furnaces. 
The  heating  resistance  or  core  should  be  given  the  largest 
possible  surface  area,  in  order  to  facilitate  the  transference 
of  its  heat  to  the  materials  of  the  furnace  charge. 

Assuming,  for  the  sake  of  example,  three  distinct  cores, 
each  of  1,200  square  millimetres  cross-sectional  area,  but 
having  different  formations,  viz.,  circular,  square,  and  rect- 
angular ;  their  efficiencies,  from  the  point  of  view  of  heat 
transference,  will  vary  considerably. 

28 


THEIR    INDUSTRIAL    APPLICATIONS 

Taking  the  diameter  of  the  first  (circular)  core  as  39  m.m., 
its  effective  surface  area,  per  metre  of  length,  will  be  132,000 
square  m.m.  The  second  (square),  with  35  m.m.  side,  will 
expose  an  area  of  140,000  square  m.m.,  for  the  same  length, 
whilst  the  third  (rectangular),  80  m.m.  by  15  m.m.,  will, 
under  similar  conditions,  have  a  surface  area  of  190,000 
square  m.m.  Their  efficiencies  will  therefore  stand  in  the 
ratio  6:7:9. 

Again,  by  constructing  the  circular  electrode  in  the  form 
of  a  hollow  cylinder,  30  m.m.,  internal,  and  46  m.m.  external 
diameter,  its  effective  surface  area  will,  for  the  same  cross- 
section  as  formerly,  be  increased  to  146,000  square  m.m. 
for  one  metre  of  length,  whilst  its  mechanical  strength  will 
be  superior  to  that  of  the  original  solid  cylinder. 

The  same  authority  quotes  the  results  of  tests  made  on 
independent  carbon  resistance  cores,  with  a  view  to  ascer- 
taining their  rate  of  oxidation,  or  combustion,  in  air. 

To  this  end,  a  current  of  500  amperes  was  passed  through 
a  rectangular  carbon  core,  400  by  80  by  15  m.m.,  which, 
with  a  gradually  increasing  current  density,  consequent 
on  the  reduction  of  its  cross-sectional  area  by  combustion, 
was  raised,  during  a  period  of  five  hours,  to  a  white  heat. 

Current  was  then  switched  off  and  the  block  examined, 
when  it  was  found  that  the  original  dimensions  of  80,  and 
15  m.m.,  had  decreased  to  60,  and  7  m.m.  respectively, 
whilst  the  under  side  of  the  block  had  been  reduced  to  a 
knife  edge  ;  the  original  cross-sectional  dimension  of  1,200 
square  m.m.  had  been  reduced  to  210  square  m.m.,  with  a 
corresponding  increase  in  current  density,  from  0*41  to  2*38 
amperes  per  square  m.m. 

A  further  test  was  then  made  with  a  view  to  ascertaining 
the  temperature  limitations  imposed  by  this  method  of 
resistance  heating  with  independent  carbon  core.  A  second 
carbon  block,  having  the  same  dimensions  as  the  first,  was 
totally  embedded  in  powdered  lime,  with  the  exception  of  its 
flat  upper  surface,  which  was  left  exposed  to  the  atmosphere. 

29 


ELECTRIC    FURNACES    AND 

A  current  of  300  amperes  was  first  applied  for  a  period  of 
15  minutes,  thus  bringing  the  temperature  of  the  carbon 
up  to  a  p.oint  suitable  for  the  commencement  of  the  tests, 
after  which  the  current  was  increased  by  regular  increments, 
at  intervals  of  five  minutes,  the  temperature  resulting  from 
each  augmentation  of  current  being  measured  by  the  col- 
lapse of  Seger  cones  placed  upon  its  exposed  surface. 

The  following  results  were  obtained  : — 


CURRENT  DENSITY  IN 

SEGER  CONE 

RESULTANT 

TEMPERATURE. 

AMPERES  PER  SQ,.  M.M. 

No. 

CENTIGRADE. 

FAHRENHEIT. 

0-25 

0-22 

590 

1,094 

0-33 

0-18 

710 

1,310 

0-45 

0-8 

990 

1,814 

0-54 

0-2 

1,110 

2,030 

0-66 

4 

1,210 

2,210 

1-2 

24 

1,600 

2,912 

1-6 

36 

1,850 

3,362 

2-0 

— 

2,300 

4,172 

The  block  was  then  replaced  by  one  of  circular  section, 
having  a  diameter  of  30  m.m.  With  this,  the  current 
density  was  increased  to  as  much  as  4  to  6  amperes  per 
square  m.m.,  without  disturbing  its  solidity. 

At   8   amperes   per  square   m.m.,   however,   the   carbon 


FIG.  9. 

commenced  to  volatilize,  though  no  intermediate  fluid 
state  was  noticed.  Its  original  diameter  was  reduced,  by 
this  treatment,  to  8  m.m. 

Furnaces. — An  early  form  of  electric  furnace  devised  by 
Borchers  may  be  taken  as  typical  of  the  resistance  principle 
of  construction.  It  consists  (Fig.  9),  of  a  cavity  A  in  the 
centre  of  a  block  of  refractory  material  B,  through  the 
sides  of  which  pass  two  large  carbon  electrodes  E  E. 

30 


THEIR    INDUSTRIAL    APPLICATIONS 

These  latter  are  fitted  with  metal  terminal  clamps  M  for 
attachment  to  the  source  of  current,  and  extend  to  a  point 
just  within  the  cavity  A,  where  their  extremities  are  bridged 
by  a  thin  carbon  pencil  C,  which  becomes  heated  by  the 
passage  of  the  current,  and  imparts  its  heat  to  the  raw 
material,  which  is  either  placed  within,  or  caused  to  pass 
through  the  cavity. 

A  modification  of  what  is  more  familiarly  known  as  the 
"  Cowles  Furnace  "  is  represented  in  Fig.  10.  It  consists 
of  a  rectangular  fire-brick  structure  F,  with  hearths  sloping 
to  a  central  tapping  hole  T.  L  is  a  lid,  fitted  with  feed 
hoppers  H  H.  The  current  enters  by  way  of  the  end 


FIG.  10. 

electrodes  E  E,  and  passes  through  the  core  C,  which 
consists  of  a  mixture  of  the  ore,  or  other  material  to  be 
treated,  with  carbon.  The  latter,  in  this  instance,  fulfils 
the  double  office  of  conductor  and  reducing  agent.  The 
core  is  surrounded  by  a  layer  of  granular  charcoal  G,  which 
conserves  the  heat  generated,  and  is,  at  the  same  time, 
highly  refractory.  The  hopper  openings  in  the  lid  L  en- 
able a  constant  and  evenly  distributed  charge  to  be  main- 
tained within  the  furnace. 

L.  S    Dumoulin's  improved  construction  for  furnaces  of 
the  independent  resistance  type  relates  to  the  resistances 

31 


ELECTRIC    FURNACES    AND 

themselves,  and  consists  in  a  means  for  protecting  them, 
and  thereby  prolonging  their  useful  life. 

To  this  end,  the  heating  resistances,  which  are  of  the 
usual  carbon  rod  type,  with  a  reduced  central  cross-section, 
where  they  come  within  the  furnace,  and  enlarged  extremi- 
ties by  which  they  are  supported  within  the  furnace  walls, 
and  to  which  the  terminal  connexions  with  the  external 
circuit  are  effected,  are  completely  encased  in  a  fire-clay 
jacket,  which  is  applied  in  a  plastic  state,  and  moulded 
around  the  resistance  rod  so  as  to  act  as  a  complete  pro- 
tection from  the  disintegrating  effects  of  the  charge  under 
treatment. 

If  necessary,  additional  protection  is  secured  by  thread- 
ing the  rods,  thus  previously  coated,  through  additional 
jackets,  or  tubes  of  fire-clay,  which  extend  through  the 
furnace  proper,  and  are,  like  the  rods  themselves,  supported 
at  their  extremities  by  the  walls  of  the  structure. 

A  resistance  furnace,  patented  by  W.  T.  Gibbs,  Canada, 
is  based  on  the  principle  of  indirect  heating,  where  the 
charge  does  not  come  into  actual  contact  with  the  heated 
resistance,  but  receives  its  heat  by  reflection  from  the  domed 
roof.  The  furnace,  which  is  too  simple  to  need  illustration, 
consists  of  a  built-up  rectangular  structure  of  carbon  blocks, 
or  fire-brick,  and  having,  as  already  stated,  a  domed  roof 
for  reflecting  the  heat  downwards  on  to  the  charge.  Suit- 
able inlet  and  outlet  orifices  are  provided,  both  for  solids 
and  gases,  while  the  heating  resistances  consist  of  carbon 
rods,  placed  transversely  across  the  furnace,  about  two- 
thirds  up,  and  clamped  between  massive  carbon  terminal 
blocks,  which  are  held,  in  turn,  by  cast  iron  sockets, 
let  into  the  walls,  and  connected  to  the  source  of  cur- 
rent. 

The  heating  capacity  of  the  Gibbs  furnace  is  governed 
by  its  size,  and  the  number  of  carbon  rod  heaters  employed, 
whilst  its  adaptability  to  currents  of  varying  character 
lies  in  the  external  means  for  changing  the  connexions  of  the 

32 


THEIR    INDUSTRIAL    APPLICATIONS 

rods,  which  may  be  either  in  series,  parallel,  or  a  combina- 
tion of  the  two. 

The  resistance  furnace  invented  by  M.  Girod,  is  capable 
of  a  wide  range  of  application,  whilst,  at  the  same  time,  of 
comparatively  simple  construction.  It  consists  of  a  cruci- 
ble of  graphite,  or  refractory  earths,  encased  on  the  outside 
by  a  graphite  sheathing,  which  serves  the  purpose  of  a  high 
resistance  path  between  the  electrodes,  and  in  which  heat 
is  developed  by  the  passage  of  a  suitable  current.  The 
structure  is  mounted  on  a  horizontal  shaft,  so  as  to  admit 
of  tipping,  or  canting,  during  operation,  after  the  manner 
of  a  Bessemer  converter.  The  voltage  necessary  ranges 
from  20  to  80,  and  the  temperature  can  be  regulated  be- 
tween 500°  and  3, 500°  C.  =  932°  and  6,332°  F.,  or  even 
higher,  if  necessary.  A  simple  furnace,  such  as  the  above 
appears  to  be,  should  be  readily  adapted  to  foundry  opera- 
tions, where  refractory  metals  have  to  be  dealt  with. 

In  the  light  of  Dr.  Nernst's  discoveries  regarding  the 
conducting  power  of  certain  solids,  when  raised  to  a  high 
temperature,  the  question  of  a  satisfactory  material  for 
the  construction  of  the  walls  of  resistance  furnaces  is  an 
important  one,  in  that,  if  the  material  chosen  be  in  the 
nature  of  a  "solid  electrolyte,"  considerable  loss  of  energy 
is  likely  to  arise  from  the  passage  of  useless  currents  through 
the  walls  of  the  structure,  when  raised  to  the  temperatures 
necessary  to  bring  about  a  re-action. 

Frohlich  seems  to  have  recognized  the  need  for  investi- 
gation in  this  direction,  and,  in  an  article  in  Zeitschrift  fur 
Elektrochemie,  August  6,  1903,  he  describes  his  investigations 
in  search  of  a  suitable  material. 

The  necessary  properties  for  such  are  a  high  melting  point, 
chemical  indifference ,  high  electrical  resistance,  and  plasti- 
city, enabling  the  substance  to  be  moulded  into  various 
shapes  and  sizes. 

He  (Frohlich)  claims  to  have  discovered  a  number  of 
chemical  compounds  which  fulfil  these  conditions,  their 

33  D 


ELECTRIC    FURNACES    AND 

electrical  resistance  being  much  higher  than  that  of  carbon, 
whilst  they  are  decomposed  but  little,  if  at  all,  by  uni- 
directional currents. 

His  sugggestion,  which  he  has  since  carried  into  practice, 
is  to  construct  conducting  plates  of  these  materials,  which, 
furnished  with  suitable  electrodes,  would  constitute  the 
heating  units  of  a  resistance  furnace  of  any  required  shape 
or  form.  The  composition  of  the  material  is  not  stated. 

In  Dr.  0.  Frohlich's  lately  patented  resistance  furnace, 
constructed  on  this  principle,  the  walls  of  the  structure 
itself  constitute  the  heating  resistances,  rendering  the  em- 
ployment of  an  independent  core  superfluous.  The  material 
used  in  the  construction  of  the  resistance  walls,  the  com- 
position of  which  is  not  divulged,  is  said  to  have  sixteen 
times  the  resistivity  of  carbon  when  hot,  and  twenty-five 
times  its  resistivity  when  cold.  A  suitable  material  has 
also  been  discovered  for  insulating  the  semi-conducting 
walls,  the  principal  merit  of  which  is  that  it  fails  to  become 
a  conductor,  even  when  raised  to  a  white  heat. 

The  furnace  is  surrounded  by  a  refractory  heat-conserving 
jacket,  an  air-space  being  left  between  the  two. 

Experimental  trials  have  demonstrated  the  possibility 
of  attaining  a  temperature  of  at  least  1,600°C.  r=2,912°F., 
by  means  of  this  furnace.  The  resistance  material  itself 
does  not  fuse  until  a  temperature  well  above  2,000°C.= 
3,632°F.,  has  been  reached. 

The  application  of  polyphase  currents  to  electric  re- 
sistance furnaces  is  the  subject  of  a  patent,  of  which  the 
details  were  published  in  1897  by  Messrs.  H.  Maxim  and 
W.  H.  Graham.  The  projected  furnace  is  of  fire-brick 
with  a  series  of  parallel  horizontal  electrodes  projecting 
through  one  of  its  walls.  These  are  connected  individually, 
through  metres  and  switches,  with  the  several  circuits  of  a 
polyphase  generator.  Opposite  their  inner  extremities, 
on  the  other  side  of  the  furnace,  is  arranged  a  common 
electrode,  to  act  as  a  return  conductor. 

34 


THEIR    INDUSTRIAL    APPLICATIONS 

For  the  manufacture  of  calcium  carbide  in  this  furnace, 
small  resistance  rods  or  pencils  of  carbon  are  so  disposed 
as  to  bridge  the  space  between  each  individual  electrode, 
and  the  common  return,  whilst  the  raw  mixture  of  coke  and 
lime  is  packed  around  them.  These  rods  become  heated 
with  the  passage  of  the  current,  and  convert  the  mixture 
into  coherent  masses  of  calcium  carbide,  which  are  subse- 
quently removed  with  the  aid  of  tongs. 

The  electrodes  are  carried  on  threaded  rods,  passing 
through  suitable  handles,  which  permit  the  necessary  with- 
drawal of  the  electrodes  pending  the  insertion  of  new  carbon 
pencils,  and,  when  in  place,  an  even  pressure  is  maintained 
by  springs. 

If  so  desired,  the  return,  or  common  electrode,  may  be 
subdivided,  and  each  pah-  enclosed  within  a  separate  com- 
partment of  the  furnace. 

A  novel  type  of  resistance,  or,  as  it  is  sometimes  termed, 
"  Induction  "  furnace,  patented  independently,  with  some 
slight  variation  of  detail,  by  Colby,  Ferranti,  and  Kjellin, 
consists  of  an  annular,  or  helical  channel,  in  a  refractory  base, 
filled  with  a  conducting,  or  semi-conducting  medium  which 
constitutes  the  furnace  charge,  and  has  a  heavy  current 
induced  in  it  by  a  surrounding  coil  of  many  turns,  carrying 
an  alternating  current. 

The  device,  in  point  of  fact,  acts  as  the  closed-circuit 
secondary  of  a  step-down  transformer,  and  is  said  to  be 
admirably  adapted  for  the  fusing  of  such  metals  as  pla- 
tinum, which,  if  exposed  to  the  atmosphere  during  the 
process,  as  in  the  ordinary  type  of  furnace,  occlude  oxygen, 
and  other  gases  in  their  mass,  which  lead  subsequently  to 
blow  holes,  and  other  imperfections  in  the  casting.  The 
Kjellin  patent  has  since  been  considerably  developed,  and 
is  now  applied  to  the  smelting  of  iron  ore  and  the  manu- 
facture of  a  special  quality  of  crucible  steel,  at  Gysinge, 
Sweden. 

The  process  is  worked  on  a  commercial  scale,  and  further 

35 


ELECTRIC    FURNACES    AND 

particulars  will  be  found  in  the  section  devoted  to  steel 
production. 

The  Acheson  Furnace  Group. — One  of  the  most  indefati- 
gable workers  in  the  field  represented  by  the  industrial 
application  of  the  resistance  furnace  is  E.  G.  Acheson,  of 
Niagara.  The  many  processes  with  which  his  name  is 
associated  as  inventor  and  originator  are  all  capable  of 
being  conducted,  with  some  slight  modifications,  in  the 
same  type  of  furnace,  which  has,  in  fact,  come  to  be  gener- 
ally known  as  the  "  Acheson  Furnace." 

The  form  of  construction  is  unique  in  being  of  a  tem- 
porary nature.  The  whole  structure  is  built  up  afresh, 
of  loose  fire-bricks,  for  each  operation,  and  pulled  down 
again  at  the  conclusion  of  a  run.  Such  a  furnace  con- 
struction offers  several  advantages  ;  it  is  not  costly  to 
construct,  is  devoid  of  all  considerations  implied  by  the 
terms,  wear  and  maintenance,  and  is,  moreover,  simplicity 
itself,  a  very  important  desideratum  in  electric  furnace 
construction. 

Carborundum. — The  manufacture  of  carborundum,  or 
carbide  of  silicon,  is  one  of  the  simplest  industrial  appli- 
cations of  the  resistance  principle.  The  furnace  itself, 
is  not  a  permanent  structure,  but  built  up  loosely  of  fire- 
brick for  each  run,  only  to  be  pulled  down  again  at  the  end 
of  the  operation.  The  process  is  purely  synthetic,  carbon, 
in  the  form  of  coke,  being  caused  to  combine,  under  stress 
of  electrical  heat,  with  the  silicon  contained  in  sand  as  an 
oxide.  The  oxygen  of  the  silica  combines  with  the  excess 
of  carbon  present,  forming  carbon  monoxide  gas,  which  is 
given  off,  and  burns  at  the  various  openings  in  the  furnace 
wall,  with  a  blue  flame.  The  silicon  thus  set  free  combines 
with  more  carbon  to  form  the  carbide. 

The  furnace,  Fig.  11,  is  built  in  the  form  of  a  species  of 
trough  T,  with  massive  electrode  clamps,  E  E,  projecting 
through  the  end  walls,  and  carrying  each  a  bundle  of  carbon 
rods  C,  which  establish  electrical  connexion  with  the 

36 


THEIR    INDUSTRIAL    APPLICATIONS 

core  proper  R  running  through  the  centre  of  the  mass. 
The  core  may  consist  of  granular  carbon,  coke,  or  the 
carbon  rods  themselves.  The  furnace  is  well  stacked  with 
the  raw  mixture  M  of  powdered  coke  and  sand,  to  which 
are  also  added  sawdust  and  a  small  quantity  of  common 
salt,  the  actual  proportions  of  each  ingredient  contained  in 
a  ten  ton  charge,  which  is  the  usual  quantity  dealt  with 
in  one  operation  at  Niagara,  being  coke,  34' 2  per  cent.  ; 
sand,  54*2  per  cent.  ;  sawdust,  9' 9  per  cent.  ;  and  common 
salt,  1*7  per  cent. 

The  object  of  the  sawdust  is  to  secure  porosity  of  the 
furnace  charge,  and  that  of  the  salt  to  act  as  a  flux. 


FIG.  11. 

The  subsequent  conversion,  which  occupies  about  thirty- 
six  hours,  results  in  some  two  tons  of  carborundum,  as  against 
a  theoretical  yield  of  four  tons,  from  which  it  will  be  seen 
that  the  process  is  anything  but  efficient. 

The  carborundum  furnaces  in  use  at  Niagara  are  15  by 
7  by  7  ft.  The  electrodes  consist  of  bundles  of  sixty 
3-in.  carbon  rods,  each  2  ft.  long.  These  are  mounted  in 
heavy  bronze  sockets,  supported  by  the  brickwork.  The 
coke  resistance  core  is  9  ft.  long  by  2  ft.  in  diameter,  and  the 
grains  of  coke  utilized  in  its  formation  vary  from  J  to  f  in. 
in  diameter.  An  alternating  current  is  employed. 

The  initial  voltage  at  the  furnace  terminals  is  200,  which, 
however,  falls  to  80  or  thereabouts  as  the  operation  pro- 
ceeds and  the  charge  becomes  heated.  Regulation  is 

37 


ELECTRIC   FURNACES    AND 

effected  by  varying  the  voltage  so  as  to  keep  the  furnaces 
working  at  their  full  capacity  of  1,000  h.p.  apiece. 

The  charge,  when  broken  up  at  the  end  of  the  run,  is 
found  to  consist  of  several  layers,  the  centre  one  of  which 
is  graphite,  into  which  the  original  coke,  or  carbon  of  the  core, 
has  been  partially  converted.  Immediately  surrounding 
this  is  a  layer,  about  16  in.  in  thickness,  of  crystallized 
carborundum,  which  constitutes  the  useful  portion  of  the 
charge,  and  consists  approximately  of  70  per  cent,  silicon, 
and  30  per  cent,  carbon.  Next  to  this  will  be  found  a 
greenish  layer  of  amorphous  silicon  carbide,  mixed  with 
unconverted  portions  of  the  charge  ;  this  layer  is  known 
as  "  white  stuff,"  and  it  is  presumable  that  its  temperatures 
of  formation  and  decomposition  are  fairly  near  together. 
The  extreme  outer  layer  consists  mainly  of  unconverted 
material,  together  with  a  somewhat  higher  percentage  of 
common  salt,  than  before,  •  that  substance  having  been 
volatilized,  and  driven  out  in  the  process  of  conversion. 
These  latter  layers  are  worked  up  again  into  the  next  charge. 

In  connexion  with  the  low  efficiency  of  the  process,  it  is 
stated  that  the  electrical  energy  necessary  for  producing 
carborundum  has  been  reduced  from  15'  5  to  8'  6  kilowatt 
hours  per  kilogramme. 

The  temperature  at  which  the  operation  is  conducted 
needs  very  careful  regulation,  in  that,  if  allowed  to  reach 
too  high  a  value,  the  carborundum  is  again  decomposed 
and  the  silicon  volatilized. 

Pure  carborundum  is  a  colourless,  crystalline  compound, 
having  the  formula,  SiC  ;  the  commercial  article  is  dark 
brown  or  black;  its  specific  gravity  is  3'  12,  and  it  con- 
sists of  70  per  cent,  silicon  and  30  per  cent,  carbon. 

Its  formation  in  the  electric  furnace  by  the  simultaneous 
reduction  of  silica,  and  synthesis  of  the  resulting  elements, 
is  represented  by  the  equation  : 


The   furnace  charge,  which  is  packed  around  the  core  of 

38 


THEIR    INDUSTRIAL   APPLICATIONS 

granulated   coke,   and  fills  up   the   entire   furnace   cavity, 
weighs  about  ten  tons,  as  already  intimated. 

Carborundum  was  first  discovered  by  Acheson  in  1893. 
In  that  year,  only  6$  tons  were  manufactured,  but,  in 
1901,  this  figure  had  been  increased  to  1,690  tons,  whilst 
an  extension  of  the  plant  (1902)  from  2,000  to  3,000  h.p. 
raises  the  possible  output  to  2,690  tons.  It  is  largely 
employed  as  an  abrasive,  a  refractory  lining  for  steel, 
and  cement  furnaces,  and  a  deoxidiser  in  steel  manufac- 
ture. 

In  connexion  with  its  use  for  lining  furnaces,  Dr.  W. 
Engels  has  lately  (1900)  patented  a  method  of  applying 
carborundum  to  the  interior  walls  of  furnaces  in  the  form 
of  a  paint.  To  this  end,  powdered  carborundum  is  mixed 
with  one- third  its  weight  of  water  glass,  and  water  added 
to  the  mixture  until  it  assumes  the  consistency  of  cream, 
in  which  form  it  is  applied  by  means  of  a  stiff  brush  to 
the  surfaces  it  is  required  to  protect.  If  the  furnace  is 
to  be  employed  in  the  treatment  of  basic  substances,  e.g. 
basic  slag,  fire-clay  is  substituted  for  the  water-glass.  It 
is  then  made  up  of  85  per  cent,  carborundum,  and  15  per 
cent,  clay,  and  applied  in  the  same  manner,  viz.,  with  a 
brush,  the  surfaces  to  be  protected  having  been  pre- 
viously dried  thoroughly  by  gentle  heating,  the  presence 
of  moisture  being  fatal  to  adhesion  of  the  coat.  1,200 
grams  of  carborundum  are  said  to  be  required  per  square 
metre  of  surface  to  be  covered. 

The  manufacture  of  what  is  known  as  "  white  stuff," 
a  material  largely  consisting  of  silicon  and  carbon,  which 
is  formed,  to  a  limited  extent,  in  the  ordinary  carborundum 
furnace,  as  a  thin  layer  between  the  carborundum  and  the 
unconverted  charge,  has  been  made  the  subject  of  a  patent 
by  Acheson.  The  respective  temperatures  of  formation  and 
decomposition  of  this  substance  are  comparatively  near 
to  one  another,  rendering  it  necessary  to  devise  a  process 
of  manufacture  in  which  these  upper  and  lower  tempera- 

39 


ELECTRIC    FURNACES    AND 

ture  limits  should  be  the  limiting  temperatures  of  the  re- 
action. Acheson  achieves  this  result  in  a  resistance  furnace 
with  subdivided  core,  consisting  of  a  number  of  equally 
spaced  carbon  rods,  distributed  throughout  the  mass  of 
the  furnace  charge.  The  success  and  efficiency  of  the 
process  depend,  of  course,  upon  the  spacing  of  these  several 
cores,  which  are  so  disposed  that  the  temperature  attained 
in  their  immediate  vicinity  is  not  in  excess  of  the  maximum 
whilst  that  at  intermediate  points  does  not  fall  below  the 
minimum  temperature  necessary  for  the  formation  of  the 
compound.  The  result  of  such  a  disposition  is  the  con- 
version of  the  entire  charge  into  "  white  stuff." 

Fitzgerald  prepares  refractory  carborundum  articles, 
such  as  crucibles,  furnace  bricks,  etc.,  by  moulding  crystal- 
lized carborundum  into  the  desired  form,  and  subsequently 
subjecting  the  articles  to  such  a  temperature,  in  the  electric 
furnace,  that  the  mass  re-crystallizes. 

F.  J.  Tone,  of  Niagara  Falls,  has  adopted  "  white  stuff," 
or  amorphous  carborundum,  to  a  similar  purpose,  the  pro- 
duct, owing  to  its  greater  porosity,  being  especially  suitable 
for  furnace  construction,  where  it  will  be  subjected  to  sudden 
and  excessive  temperature  changes.  A  temporary  binder 
of  glue,  or  water-glass,  is  added  to  the  mass  previous  to 
moulding,  and  the  articles  may  be  conveniently  heated 
by  embedding  them  in  the  usual  charge  of  a  carborundum 
furnace. 

Siloxicon  is  the  name  given  to  a  new  class  of  compounds, 
the  commercial  value  and  mode  of  preparation  of  which 
have  been  recognized  and  patented  by  Acheson,  and 
assigned  to  the  Acheson  Company  of  Niagara  Falls. 

Generally  speaking,  it  consists  of  carbon,  silicon,  and 
oxygen  in  chemical  combination,  and  is  described  as 
amorphous,  grey-green,  when  cold,  and  light  yellow  when 
heated  to  149°C.=300°F.  or  above;  density  2' 75  ;  very 
refractory  to  heat ;  insoluble  in  molten  iron ;  neutral 
towards  acid  and  basic  slags  ;  indifferent  to  all  acids  save 

40 


THEIR    INDUSTRIAL   APPLICATIONS 

hydrofluoric  ;  unattacked  by  hot  alkaline  solutions,  and 
self-binding  to  such  a  degree  that  the  use  of  a  separate 
binding  agent  is  not  essential  in  forming  it  into  crucibles, 
furnace-linings,  fire-bricks,  and  such  other  articles  as  may 
be  manufactured  from  it.  The  articles  may  be  formed  by 
merely  moistening  the  pulverulent  material  with  water, 
moulding,  and  firing,  or,  if  desired,  a  carbonaceous  or  other 
binding  material  may  be  used. 

It  is  a  by-product  of  the  process  of  carborundum  manu- 
facture, and  is  prepared  in  an  Acheson  resistance  furnace 
with  multiple  core.  The  manufacture  of  siloxicon  bears 
a  striking  resemblance  to  that  of  carborundum.  The 
process  is  patented  by  E.  G.  Acheson,  and  is  being  worked 
by  the  Acheson  International  Graphite  Company.  The 
raw  materials  are  ground  coke  and  sand,  mixed  in  the 
proportion  of  one  part  carbon  to  two  parts  silicon,  with  a 
certain  quantity  of  sawdust  to  impart  porosity  to  the  mass. 
In  adding  the  latter,  due  regard  is  paid  to  its  carbon  con- 
tent ;  the  correct  apportioning  of  the  carbon  percentage 
in  the  furnace  charge  is  of  great  importance,  as,  if  it  be 
present  in  excess,  the  silica  will  be  completely  reduced, 
and  no  formation  of  siloxicon  will  take  place.  Siloxicon 
has  a  chemical  composition  approximately  represented 
by  the  formula  Si2C20. 

As  in  the  case  of  carborundum  manufacture,  the  furnace 
is  loosely  built  of  fire-brick,  its  approximate  dimensions 
being  :  length,  30  ft.  ;  width,  8  ft.  ;  and  depth,  6  ft.  To 
operate  a  siloxicon  furnace  of  this  capacity  1,000  e.h.p. 
are  required. 

The  original  siloxicon  furnace  had  a  double  flat  heating 
core,  but  the  writer  understands  that  later  furnaces  have 
been  constructed  with  three  cores. 

The  temperature  at  which  the  reaction  takes  place  is 
lower  than  that  required  for  the  production  of  carborundum, 
the  formation  of  siloxicon  occurring  at  a  temperature 
between  2,480°  and  2,757°C.=  4,500°  and  5,000°F.,  whereas 

41 


ELECTRIC   FURNACES    AND 

carborundum  manufacture  entails  a  temperature  of  approx- 
imately 3,876°C.  =  7,000°F. 

Freshly  made  siloxicon  is  a  greyish  green,  loosely  co- 
herent mass,  and,  on  leaving  the  furnace,  it  is  subjected 
to  a  milling  process  which  reduces  it  to  such  a  grade  that 
it  will  pass  through  a  No.  40  sieve. 

It  is  a  self-binding  material,  and  only  needs  forming 
into  a  paste  with  water,  when  it  can  be  moulded  into  any 
desired  form,  which  is  rendered  permanent  by  subsequent 
firing.  For  some  purposes,  an  admixture  of  25  per  cent. 
clay  may  be  introduced  into  the  mass,  prior  to  moulding, 
or,  if  preferred,  additional  binding  materials,  such  as  liquid 
tar,  asphaltum,  pitch,  molasses  or  glue  ;  in  fact,  any  similar 
carbonaceous  binding  material  may  be  employed,  in  which 
case  the  siloxicon  powder  and  agglutinant  are  thoroughly 
mixed  whilst  hot,  after  which  the  mixture  is  moulded  into 
the  desired  form  and  burned,  or,  as  an  alternative,  may  be 
used  without  burning,  the  subsequent  heating  to  which  it 
is  subjected  in  use  being  sufficient  for  the  purpose. 

It  has  a  promising  future  in  the  manufacture  of  all 
kinds  of  refractory  articles,  such  as  furnace  linings, 
crucibles,  fire-bricks,  etc. 

For  lining  furnaces,  the  paste  or  mixture,  prepared  as 
above,  is  applied  to  the  surface  to  be  protected,  and  well 
rammed  into  place,  where  subsequent  burning  converts  it 
into  a  homogeneous  refractory  layer. 

Siloxicon,  when  heated  to  a  temperature  of  1,466°C.  = 
2,674°F.,  or  above,  in  an  atmosphere  containing  free 
oxygen  in  excess,  decomposes,  presumably,  according  to 
the  equation  : 

+  70=2Si02 


If  the  siloxicon  thus  heated  be  agglomerated  or  moulded 
into  a  coherent  mass,  the  reaction  is  confined  to  the  surface 
of  the  latter,  and  produces  a  vitreous  glaze,  tinged  light 
green  by  the  presence  of  iron  as  an  impurity.  In  the  absence 

42 


THEIR    INDUSTRIAL   APPLICATIONS 

of  free  oxygen,  or  in  a  reducing  atmosphere,  no  decomposi- 
tion occurs  at  the  above  temperature,  and  the  siloxicon 
may  be  heated  to  the  formation  temperature  of  carborun- 
dum, approximately  3,867°C.=7,000°F.,  without  change. 
At  this  point,  however,  it  dissociates  ;  the  equation  repre- 
senting its  decomposition  is  supposed  by  Acheson  to  be  : 

Si2C20=SiC+Si  +  CO. 

Solid  carborundum  is  left  behind,  whilst  siloxicon  vapour 
and  carbon  monoxide  gas  are  driven  off.  Carborundum, 
subjected  to  the  same  treatment,  behaves  similarly. 

Artificial  Graphite. — The  electric  furnace  devised  by 
E.  G.  Acheson  for  the  manufacture  of  graphite  is,  like  the 
other  designs  which  owe  their  origin  to  his  inventive  genius, 
of  the  resistance  type.  It  takes  the  form  of  a  trough-like 
structure,  in  which  is  placed  the  rough  charge  of  anthracite 
coal,  or  coke,  which  it  is  required  to  convert  into  graphite. 
The  core  is  independent  of  the  charge  itself,  and  consists 
of  a  series  of  carbon  rods,  extending  through  the  mass  to 
be  heated,  and  forming  a  bridge  for  the  current  between 
two  end  electrodes.  The  raw  charge  itself  is,  at  first,  a 
non-conductor,  and  the  current,  when  switched  on,  passes 
entirely  through  the  carbon  rods,  raising  them  to  a  high 
temperature.  The  heat  thus  evolved  converts  the  layer  of 
coal  or  coke,  immediately  surrounding  the  core,  into  graphite, 
which,  in  turn,  becomes  a  conductor,  and  performs  a  similar 
office  for  the  next  layer  of  raw  material,  and  so  on  until 
the  whole  charge  has  been  converted. 

A  study  of  the  various  allotropic  modifications  of  carbon, 
and  the  changes  they  severally  undergo  when  subjected 
to  high  temperatures,  provides  a  wide  and  interesting  field 
for  the  investigator,  and  many  scientists,  past  and  pre- 
sent, recognizing  the  possibilities  opened  up  by  a  more 
advanced  knowledge  of  the  subject,  have,  from  time  to 
time,  devoted  considerable  attention  to  it.  The  principal 
results  of  their  experiments,  in  so  far  as  they  bear  upon 

43 


ELECTRIC    FURNACES    AND 

the  artificial  production  of  graphite,  have  been  assembled 
in  the  form  of  a  very  interesting  article  by  C.  P.  Townsend, 
which  appeared  in  the  Electrical  World,  April  6,  1901, 
and  to  which  the  reader  is  directed  for  the  original  refer- 
ences. The  writer  has  taken  the  liberty  of  extracting 
therefrom  the  following  interesting  and  salient  points  in 
the  history  of  the  manufacture  of  artificial  graphite. 

Scheele,  as  far  back  as  1778,  discovered  the  solvent 
power  of  molten  iron  for  carbon,  and  also  the  additional 
fact  that  a  portion  of  the  carbon  so  dissolved  separates  out 
on  cooling  in  the  form  of  graphite,  a  discovery  which  has 
since  exercised  an  important  influence  upon  the  iron 
industries. 

This  knowledge  was  further  supplemented  in  1896  by 
Moissan,  who  showed  that  the  purity  of  the  graphite  thus 
formed  by  separation  on  the  cooling  of  the  iron  solvent 
is  proportional  to  the  temperature  to  which  the  solvent 
metal  has  been  raised,  and  to  the  pressure  exerted  by  the 
iron  in  cooling.  Moreover,  it  has  been  demonstrated  that 
graphite,  from  whatever  source,  invariably  contains  hydro- 
gen as  a  constituent,  though  not,  apparently,  in  chemical 
combination  with  it. 

In  1849  Despretz  commenced  a  series  of  careful  inves- 
tigations into  the  changes  undergone  by  carbon  at  high 
temperatures,  his  apparatus  consisting  of  a  closed  cast-iron 
furnace,  through  the  walls  of  which,  and  rendered  air- 
tight by  leather  stuffing  boxes,  projected  two  carbon 
electrodes. 

Inlet  and  outlet  pipes  for  the  introduction  and  with- 
drawal of  gases  were  provided,  and  the  effects  of  variations 
in  the  pressure  duly  noted. 

This  experimental  furnace  was  operated  both  on  the  "  arc  " 
and  "  resistance "  principles,  by  the  current  from  600 
Bunsen  cells,  in  series  of  25,  50,  or  100,  as  occasion  deter- 
mined. 

Various  forms  of  carbon  were  experimented  upon,  and 

44 


THEIR    INDUSTRIAL    APPLICATIONS 

Despretz    thus   summarized    the    results    of   his    investiga- 
tions— 

(1)  Carbon,    in  a  vacuum,   volatilizes    at    temperatures 
produced   by    500   to    600   Bunsen   cells.     Under   pressure 
of  nitrogen  at  2|  atmospheres,  volatilization  occurs  more 
slowly. 

(2)  Carbon,  at  these  temperatures,  may  be  bent,  welded, 
or  fused. 

(3)  Carbon  from  all  sources  becomes  progressively  softer, 
finally  turning  to  graphite. 

(4)  Graphite  volatilizes  slowly. 

(5)  Diamond  is  converted  into  graphite. 

Strangely  enough,  this  early  investigator  appears  to  have 
actually  applied  the  modern  principles  of  artificial  graphite 
manufacture,  and  yet  failed  to  produce  it,  for  he  asserts, 
in  the  course  of  his  report  : — "  I  have  enveloped,  I  have 
impregnated,  acicular  rods  of  carbon,  with  more  fusible 
materials,  silica,  alumina,  magnesia,  to  determine  whether 
the  presence  of  a  more  fusible  body  would  render  the  fusion 
of  the  carbon  more  easy.  The  silica,  magnesia,  and  alumina, 
escaped  as  vapours  and  the  carbon  remained  unmodified." 

In  the  case  of  anthracite  coal,  however,  Despretz  appears 
to  have  met  with  a  measure  of  success,  for  he  speaks  of  its 
conversion  into  "  well  characterized  graphite,"  the  con- 
version having  been  effected  in  a  crucible  by  the  heat  of 
an  arc  struck  between  an  independent  electrode  and  the 
anthracite  under  treatment. 

In  1870  Berthelot  studied  the  direct  combination  and 
conversion  of  carbon  ;  he  was  unable  to  effect  the  conver- 
sion of  amorphous  carbon  into  graphite  by  any  other  heat 
save  that  of  the  arc,  nor  could  he  convert  graphite  into 
amorphous  carbon.  Berthelot  was  responsible  for  the 
discovery  that  graphite  could  be  obtained  as  the  result  of 
decomposing  a  carbide.  He  heated  boron  carbide  in  an 
atmosphere  of  dry  chlorine  gas,  and  found  that  at  a  tempera- 
ture below  the  softening  point  of  glass,  carbon  separates 

45 


ELECTRIC    FURNACES    AND 

out  as  amorphous  graphite,  and,  at  the  fusing  point  of  porce- 
lain as  hexagonal  crystals. 

In  1893  Girard  and  Street  introduced  their  system  of 
superficially  graphitizing  electrodes  and  other  carbon 
articles,  by  causing  an  arc  or  arcs  to  play  over  the  entire 
surface  of  the  object,  the  process  being  carried  out  either 
in  an  atmosphere  of  carbon  monoxide,  nitrogen,  or  similarly 
neutral  gas,  or  in  a  vacuum. 

In  1896  Moissan  pointed  out  that  diamond,  when  sub- 
jected to  the  heat  of  the  arc,  was  converted  into  graphite, 
a  conclusion  previously  arrived  at  by  Despretz.  Moissan 
also  investigated  the  solution  of  carbon  by  many  metals, 
and  its  subsequent  separation  as  graphite,  on  cooling. 
Among  the  metals  experimented  with,  were  aluminium,  silver, 
manganese,  nickel,  chromium,  tungsten,  molybdenum, 
uranium,  zirconium,  vanadium,  titanium  and  silicon. 

At  normal  pressures,  carbon  has  no  intermediate  liquid 
state. 

The  results  of  Moissan's  varied  and  extensive  researches 
on  the  subject  of  graphite  and  its  formation  have  been 
thus  summarized  by  him  (Comptes  Rendus,  vol.  119,  p.  980) — 

1.  Whatever  the  variety  of  carbon,  elevation  of  tempera- 
ture   always    suffices    to    convert    it    into    graphite.     This 
graphite  may  be  amorphous,  or  crystallized,  has  a  specific 
gravity  of  2' 10  to  2' 25,  and  a  temperature  of  combustion 
in  oxygen  of  660°C.=1,220°F. 

2.  There  are  several  varieties  of  graphite,  just  as  there  are 
several  varieties  of  amorphous  carbon  and  of  the  diamond. 

3.  The  stability  of  graphite  (its  resistance  to  oxidation) 
increases  in  proportion  to  the  temperature  to  which  it  has 
been  subjected. 

4.  This  fact  is  clearly  shown  by  the  resistance  opposed 
by  different  graphites  to  transformation  to  graphitic  oxide. 
The  difficulty  of  this  oxidation  increases  in  proportion  to 
the  fusing  point  of  the  metal,  from  solution  in  which  the 
graphite  has  been  derived.     Similarly,  a  readily  oxidizable 


THEIR    INDUSTRIAL    APPLICATIONS 

graphite,  like  that  of  Ceylon,  becomes  much  more  resistant 
after  heating. 

Acheson,  who  is  associated  with  the  most  modern  methods 
of  treating  carbon  and  certain  of  its  compounds  in  the  electric 
furnace,  patented,  as  early  as  1895,  a  process  of  coke  puri- 
fication, which  consists  in  subjecting  it  to  the  direct  heat 
of  the  current,  thus  volatilizing  the  impurities  and  leaving 
the  carbon  in  a  practically  pure  state,  and,  in  all  probability 
partially  converted  into  graphite.  In  the  same  year,  he 
patented  a  method  for  the  production  of  graphite  by  the 
decomposition  of  silicon  carbide  (carborundum),  that  com- 
pound being  heated  to  such  an  extent  as  to  volatilize  the 
silicon.  Moissan  has  similarly  produced  graphite  by  the 
high  temperature  decomposition  of  calcium  carbide,  em- 
ploying a  1,200  ampere,  60  volt,  arc  furnace. 

In  1899  Acheson,  who  may  be  regarded  as  an  authority 
with  considerable  practical  experience  of  his  subject, 
published  in  the  Journal  of  the  Franklin  Institute  his 
observations  on  the  yield  of  graphite,  and  the  conclusions 
to  be  drawn  therefrom.  They  run  as  follows — 

1.  Comparatively   pure   petroleum   coke   produces   prac- 
tically no  graphite. 

2.  Impure  bituminous  coal  coke  produces  large  quantities 
of  graphite. 

3.  The  larger  the  percentage  of  impurities  in  the  bitumin- 
ous coal  core,  the  greater  the  yield  of  graphite. 

4.  Only  part  of  the  carbon  core  of  carborundum  furnaces 
is    converted   into   graphite    (that   part   which  carries    an 
admixture  of  slate,  or  a  high  ash  content).     This  conversion 
is  not  increased,  even  by  repeated  use  of  the  same  grains  in 
successive  furnaces. 

The  conclusions  drawn  by  Acheson  from  these  observa- 
tions are — 

1.  Graphite — is  the  form  carbon  assumes  when  freed  from 
chemical  associations,  under  conditions  of  low  pressure 
and  protection  from  chemical  influence. 

47 


ELECTRIC    FURNACES    AND 

2.  Diamond — is  the  form  carbon  assumes  when  freed  from 
chemical  associations,  under  the  conditions  of  high  pressure 
and  protection  from  chemical  influence. 

And,  by  "  inference  " 

3.  Amorphous  carbon — is  the  form  carbon  assumes  when 
freed  from  chemical  associations,  under  conditions  of  high 
or  low  pressure  and  exposure  to  chemical  influence. 

It  will  have  been  noted,  from  the  foregoing  context,  that 
these  various  investigators  are  far  from  being  of  one  accord 
as  regards  the  theory  of  the  formation  of  graphite.  Com- 
menting upon  this,  and  basing  his  deductions  upon  the  fact 
that  Moissan,  with  an  arc  furnace,  succeeded  in  converting 
all  forms  of  carbon  into  graphite,  whereas  Acheson,  working 
with  his  well  known  resistance  type  of  furnace,  failed  to 
effect  such  conversion  in  the  case  of  pure  carbon,  Townsend 
suggests  that  the  preliminary  ionization  of  the  carbon  is 
essential  to  the  formation  of  graphite  ;  he  thus  advances 
his  theory — 

"  The  essential  condition  for  the  formation  of  graphite 
may  be  considered  to  be  the  presence  of  carbon  in  the 
ionized  state,  and  its  separation  therefrom.  This,  so  far 
as  we  know,  may  be  accomplished  by  any  one  of  four 
methods — 

"1.  By  solution  in  metals  or  carbides. 

"  2.  By  the  direct  ionizing  action  of  the  electric  discharge, 
and  notably  the  arc,  upon  carbon. 

"3.  By  the  action  of  the  electric  discharge  upon  gaseous 
carbon  compounds. 

"4.  By  the  dissociation,  by  heat,  of  certain  carbon 
compounds,  notably  the  carbides." 

Borchers  and  Mogenburg,  investigating  the  conversion 
of  amorphous  carbon  into  graphite  by  electric  furnace 
methods,  have  also  found  the  process,  with  pure  carbon, 
very  difficult  of  accomplishment.  The  conversion  is, 
however,  facilitated  by  the  presence  of  metals  or  their 
compounds,  notably  aluminium.  These  combine  with  the 


THEIR   INDUSTRIAL   APPLICATIONS 

carbon  to  form  carbides,  which  are  subsequently  decomposed, 
and  the  carbon  released  from  combination  in  the  form  of 
graphite.  The  quantities  of  metal  thus  required  are  very 
small,  and  aluminium  has  been  found  most  suitable  and 
effective  for  the  purpose. 

In  the  course  of  his  researches  into  the  manufacture  of 
artificial  graphite,  Acheson  has  demonstrated  that  the 
carbide  forming  impurities  need  not  be  present  in  propor- 
tion sufficient  to  react  at  once  with  the  whole  of  the  carbon 
to  be  converted,  but  that  the  graphite  formation  may  be  of 
a  progressive  character,  small  quantities  of  carbide  being 
formed,  decomposed,  and  the  volatilized  impurity  again 
combine  with  an  adjacent  portion  of  carbon,  to  repeat  the 
cycle  of  transformation. 

He  also  found  that  the  introduction  of  additional  carbide 
forming  impurities,  in  the  case  of  non-coking  coal,  and 
certain  kinds  of  charcoal,  was  unnecessary,  in  that  they 
contained  sufficient  mineral  impurities  in  themselves  to 
effect  their  conversion  into  graphite,  when  raised  to  the 
required  temperature. 

It  is  not  essential  that  the  preliminary  mixing  in  of  the 
impurities  with  the  mass  of  carbon  be  thorough,  as  the 
metallic  vapours  formed  during  the  process  thoroughly 
permeate  the  entire  mass. 

According  to  Blount  (Paper  read  before  Manchester 
Section  I.E.E.,  March  4,  1902)  there  are  three  methods 
available  for  the  artificial  manufacture  of  graphite  in  the 
electric  furnace. 

1.  By  direct  conversion  at  a  very  high  temperature. 

2.  By   crystallization,    on   cooling,   from   supersaturated 
solution  of  carbon  in  some  suitable  metal  (e.g.,  aluminium, 
manganese,     nickel,     chromium,     tungsten,     molybdenum, 
uranium,  zirconium,  vanadium  and  titanium). 

3.  By  crystallization  of  dissolved  carbon  from  its  metallic 
solution,  by  the  addition  of  an  element,  such  as  silicon  or 
boron,  capable  of  displacing  it. 

49 


J^\  \  &  R  A  ft  rSfe 
u  or  THIE 

(  UNIVERSITY  ) 


ELECTRIC    FURNACES    AND 

Blount,  in  speaking  of  Acheson's  method  of  manufacturing 
artificial  graphite,  criticizes  the  wording  of  his  patent  claims, 
which  nominally  cover  the  production  of  graphite  by  the 
decomposition  of  a  carbide,  and  points  out  that,  if  put  to 
the  test  in  a  patent  litigation  case,  they  would  probably 
prove  untenable,  in  that  they  refer  to  processes  discovered 
and  made  public  many  years  ago.  In  this  connexion  it 
may  be  mentioned  that  Acheson's  own  theory  to  account 
for  the  conversion  of  amorphous  carbon  into  graphite  at 
high  temperatures  is  that  it  follows  from  the  decomposition 
of  a  carbide,  which  is  formed  in  the  first  instance,  the  carbon 
of  the  latter  being  deposited  in  the  form  of  graphite. 

A  good  mixture  for  the  production  of  artificial  graphite 
is  said  to  consist  of  97  parts  finely  divided  amorphous  carbon 
mixed  with  three  parts  iron  oxide.  It  is  suitable  for 
moulding  into  any  desired  form  previous  to  graphitizing. 

The  output  of  artificial  graphite  in  America  was  81  tons 
in  1897  ;  in  1901,  it  had  increased  to  1,200  tons. 

The  total  yearly  production  of  the  International  Acheson 
Graphite  Co.  alone,  in  1902,  was  said  to  be  in  the  neigh- 
bourhood of  500  tons. 

Graphitizing  Electrodes. — The  Acheson  resistance  furnace 
for  graphitizing  electrodes,  as  employed  at  the  works  of  the 
International  Acheson  Graphite  Company,  Niagara  Falls, 
is  of  the  usual  type,  as  already  described  in  connexion  with 
the  manufacture  of  carborundum.  The  process  of  graphitizing 
is  similar  to  that  already  dealt  with,  and  consists  in  causing 
the  pure  carbon,  under  the  influence  of  electric  heat,  to 
combine  with  certain  carbide  forming  impurities  which  are 
present  in  the  mass  prior  to  the  process. 

The  electrodes  are  first  made  up  in  the  usual  way,  from 
petroleum  coke  and  pitch,  like  ordinary  arc  light  carbons, 
the  only  addition  being  a  certain  amount  of  carbide- forming 
material  such  as  silica,  or  iron  oxide.  They  are  baked  in 
the  usual  way,  and  then  subjected  to  the  graphitizing 
furnace,  in  which  process  they  are  raised  to  a  temperature 

50 


THEIR    INDUSTRIAL    APPLICATIONS 

well  above  that  of  the  volatilization  of  iron,  aluminium, 
or  silicon. 

The  necessary  temperature  for  the  reaction  is  higher  than 
that  required  for  the  decomposition  of  the  carbides  formed, 
and  is  produced  in  the  furnace  construction  represented 
in  Fig.  12,  where  F  is  the  outer  rectangular  structure  of 
fire-brick,  through  the  end  walls  of  which  are  introduced 
the  electrodes  e  e,  which  conduct  the  current  to  the  charge  C ; 
this  latter  may  either  consist  of  cylindrical  rods,  as  repre- 
sented in  transverse  section  in  the  figure,  or  rectangular 
plates.  In  the  former  case  the  rods  are,  as  shown,  packed 
transversely  to  the  direction  of  current  flow,  the  necessary 


FIG.   12. 

high  resistance  path  from  one  to  the  other  being  estab- 
lished along  the  lines  of  contact  between  the  cylindrical 
surfaces. 

It  is  chiefly  along  these  lines  that  the  heat  is  generated, 
and  this  mode  of  packing  the  articles  to  be  graphitized 
gives  rise  to  the  evolution  of  heat  exterior  to  the  articles, 
rather  than  in  the  mass  itself,  as  would  be  the  case  were 
they  arranged  with  their  axes  parallel  to  the  line  of  direction 
of  the  current.  This  constitutes  the  principal  feature  of 
the  invention,  and  effects  considerable  economy  in  the 
current  required  for  the  operation  of  the  furnace. 

If  the  objects  to  be  graphitized  are  rectangular,  they  are 
arranged  in  a  series  of  regular  piles  along  the  path  of  the 
current,  each  pile  being  separated  from  its  neighbour  by 
a  filling  of  ground  or  pulverized  coke. 

The  latter  is  also  employed  as  a  filling,  in  both  cases,  and 

51 


ELECTRIC    FURNACES    AND 

is  introduced  between  the  ends  of  the  charge  and  the  elec- 
trodes. The  base  of  the  furnace  is  lined  with  a  refractory 
layer  of  carborundum  R,  or  similar  conducting  material, 
and  the  whole  is  covered  in  at  the  top  with  a  layer  of  ground 
coke  and  sand  S. 

One  of  the  latest  resistance  furnace  methods  patented 
by  Acheson  relates  to  the  manufacture  or  baking  of 
moulded  carbon  articles,  such  as  electrodes,  arc-light 
carbons,  etc.  To  this  end  they  are  embedded  in  a  heating 
resistance  composed  of  granular  carbon,  or  a  mixture  of 
carbon  with  silicon,  etc.  The  articles  to  be  baked  are 
placed  with  their  longest  dimensions  at  right  angles  to  the 
path  of  the  current,  as  in  the  foregoing  graphitizing  furnace, 
and  the  principle  of  the  method  consists  in  confining  the 
evolution  of  heat  to  the  resistance  core  of  packing,  rather 
than  to  the  articles  themselves.  A  very  uniform  and  easily 
regulable  heating  effect  is  said  to  be  obtained  in  this  manner. 

Coke  Purification. — It  is  necessary  that  the  carbon  used 
in  electro-metallurgical  operations  be  pure,  and,  more 
especially,  free  from  silica  and  the  compounds  of  silicon, 
which  would,  if  present,  combine  with  the  metal  under 
treatment,  and  result  in  the  re-introduction  of  like  impuri- 
ties into  the  finished  article. 

Mr.  C.  M.  Hall,  the  patentee  of  the  aluminium  process 
which  bears  his  name,  has  devised  and  patented  a  form  of 
resistance  furnace  for  ridding  the  coke  of  these  undesirable 
impurities  before  it  is  employed  in  connexion  with  the 
extraction  of  metals. 

The  process  consists  in  powdering  the  coke,  and  mixing 
it  intimately,  whilst  thus  powdered,  with  a  metallic  fluoride, 
such  as  sodium  fluoride,  cryolite,  or  fluor-spar.  This 
mixture,  when  subjected  to  heat  in  a  suitable  furnace, 
becomes  pure  carbon,  owing  to  the  reaction  set  up  between 
the  fluoride  and  the  compounds  of  silicon,  which  combine 
to  form  silicon  fluoride,  the  latter  being  driven  off  in  the 
form  of  gas. 

52 


THEIR    INDUSTRIAL    APPLICATIONS 

By  adding  a  suitable  proportion  of  pitch  to  the  mixture, 
as  a  binding  material,  it  can  be  moulded  into  electrodes  of 
any  desired  form,  and  the  purification  and  baking  process 
carried  out  in  one  operation  of  the  furnace. 

The  latter  is  built  of  brick,  and  filled  with  moulded  carbon 
blocks,  packed  symmetrically,  and  insulated  from  one 
another  by  suitable  packing.  Through  the  centre  of  the 
mass,  and  in  close  proximity  to  the  blocks,  runs  a  resistance 
core  with  end  electrodes.  An  alternating  current  is  supplied 
to  this  core  by  means  of  the  electrodes,  and  the  heat  ad- 
justed to  any  desired  temperature,  by  varying  the  current. 

The  actual  temperature  is  necessarily  slightly  higher  than 
that  required  for  baking  alone,  in  order  to  produce  the 
necessary  thermo-chemical  action  for  the  purification  of 
the  carbon. 

Peat  Coal. — Of  late  years  the  problem  of  adapting  peat 
to  the  same  fuel  uses  as  coal  has  engaged  considerable 
attention,  and  several  processes  for  manufacturing  what  is 
known  as  "  Peat  Coal  "  have  been  evolved.  In  this  con- 
nexion the  possibilities  of  electric  heating  have  not  been 
overlooked. 

The  Jebsen  process,  invented  by  P.  Jebsen,  Norway, 
and  commercially  exploited  by  him  at  Stangfjorden,  has 
been  in  successful  practice  for  over  three  years.  The  peat 
is  first  kneaded  and  compressed  into  rectangular  blocks  by 
special  machinery,  after  which  it  is  subjected  to  a  drying 
process,  by  exposure  to  blasts  of  the  hot  gases  produced 
in  the  carbonizing  retorts.  These  gases,  which  have  an 
initial  temperature  of  from  90°  to  100°C.  =  194°  to  212°F., 
reduce  the  quantity  of  moisture  present  in  the  peat  from 
80  per  cent,  to  25  per  cent,  or  thereabouts. 

It  is  then  ready  to  undergo  the  electrical  carbonization 
process,  which  is  carried  out  in  what  is  virtually  a  resistance 
furnace  with  independent  cores.  Each  furnace  or  retort, 
consists  of  an  iron  cylinder,  about  six  feet  long,  by  three 
feet  in  diameter,  with  removable  end  covers.  These 

53 


ELECTRIC  FURNACES   AND 


retorts  are  mounted  in  a  vertical  position  and  lined  interiorly 
with  asbestos  or  fire-brick. 

The  heating  resistances  are  in  spiral  form,  supported 
from  the  walls  of  the  retort,  and  so  disposed  that  the  peat 
under  treatment,  when  packed  into  the  cavity,  comes  into 
intimate  contact  with  them.  The  disposition  is  such  that 
practically  all  the  heat  evolved  is  utilized  and  absorbed  by 
the  peat,  the  loss,  by  radiation,  being,  to  all  practical 
intents  and  purposes,  nil.  Experience  has  determined  the 
time  and  current  necessary  to  effect  the  carbonization  process, 
after  which  the  current  is  switched  off,  and  the  retort,  with 
its  charge,  allowed  to  cool.  The  lower  cover  is  then  removed, 
and  the  carbonized  peat  allowed  to  fall  into  a  truck  placed 
to  receive  it. 

The  temperature  required  to  thoroughly  effect  the  car- 
bonization is  from  400°  to  500°C.=752°  to  932°F.  By 
lengthening  the  retorts,  the  process  can  be  made  continuous, 
the  dried  peat  being  continuously  fed  in  above  and  the  car- 
bonized product  removed,  periodically,  from  below. 

The  Jebsen  process  of  peat  coal  manufacture  results  in 
several  marketable  by-products,  among  which  may  be  men- 
tioned peat  oil,  paraffin,  gas  oil,  coke,  and  gas,  the  latter 
being  utilized,  as  already  stated,  in  the  preliminary  drying 
of  the  peat.  The  peat  coal  produced  by  this  process  has  a 
heating  value  of  7,500  calories,  burns  with  intense  heat,  and 
produces  very  little  ash,  or  soot.  Samples,  subjected  to 
analysis  at  the  Royal  Norwegian  High  School,  in  Christiania, 
showed  the  following  composition — 


Carbon 

Hydrogen 

Oxygen 

Nitrogen 

Sulphur 

Ashes 

Humidity 


76-91  per  cent. 
4-64 
8-15 
1-78 
•70 
3-00 
4-82 

100-00 


54 


THEIR   INDUSTRIAL   APPLICATIONS 

Peat  carbon,  produced  by  the  Jebsen  process,  is  said  to 
be  especially  suited  for  calcium  carbide  manufacture.  The 
product  of  the  process  is,  roughly,  33  per  cent,  charcoal, 
4  per  cent,  tar,  40  per  cent,  liquor,  and  23  per  cent,  gas, 
the  figures  being  based  on  the  treatment  of  initially  dried 
peat.  The  carbon  is  very  hard,  and  of  a  deep  black  colour. 
The  current  necessary  for  the  process  is  derived  from  five 
80  k.w.  generators  driven  by  turbines  of  128  h.p. 

A  process  analogous  to  that  of  Jebsen,  but  not  carried 
to  such  a  high  degree  of  carbonization,  has  been  invented 
by  Mr.  Bessey,  and  was  publicly  demonstrated  before  a 
committee  of  press  representatives  and  technical  experts, 
at  the  works  of  Messrs.  Johnson  and  Phillips,  Charlton, 
Kent,  in  1903. 

The  peat  is  first  placed  in  a  centrifugal  drying  apparatus, 
which  drives  out  a  considerable  portion  of  the  80  per  cent, 
moisture  which  it  contains.  Electrodes  are  then  introduced, 
and  the  drying  pushed  to  a  higher  degree  by  the  resistance 
process  of  electrical  heating,  the  necessary  initial  conduc- 
tivity of  the  mass  being  secured  by  the  addition  of  certain 
chemicals. 

A  company,  known  as  the  Electro-Peat-Coal  Syndicate, 
has  since  been  formed  for  the  purpose  of  exploiting  this 
process  on  a  commercial  scale,  and  it  is  estimated  that  peat 
coal  can  be  produced  at  a  cost  of  5s.  per  ton  inclusive. 

Carbon  Bisulphide. — The  resistance  furnace  utilized  in 
the  manufacture  of  carbon  bisulphide  at  Penn  Yan,  N.Y., 
U.S.A.,  is  illustrated  in  Fig.  13.  It  is  the  invention  of 
Mr.  E.  R.  Taylor,  and  is  the  outcome  of  considerable  fore- 
thought and  experiment.  In  the  original  furnaces,  inde- 
pendent carbon  electrodes  were  utilized  as  terminals,  being 
protected  from  a  too  rapid  combustion  by  broken  carbon, 
which  was  fed  into  the  furnace  through  orifices  immediately 
surrounding  the  electrodes.  In  the  latest  type  of  furnace 
the  carbon  block  terminals  have  been  entirely  dispensed 
with,  electrical  connexion  being  made  directly  with  the 

55 


ELECTRIC   FURNACES    AND 


carbon  feed  hoppers,  through  which  the  broken  carbon  is 
introduced  into  the  furnace. 

In  brief,  the  action  is  as  follows :  the  upper,  cylindrical 
portion  is  filled  with  closely  packed  carbon  C,  through 

which  the  sulphur  vapours, 
produced  by  the  action  of 
electric  heat  upon  the 
fused  mixture  of  carbon 
and  sulphur,  F  at  the 
hearth  of  the  furnace,  rise, 
and  in  passing  are  con- 
verted into  carbon  bisul- 
phide, which  is  suit- 
ably collected  and  con- 
densed. 

Terminal  con  n  e  x  i  o  n 
with  the  furnace  is  se- 
cured through  the  carbon 
hoppers  M  M,  which  are 
four  in  number,  situated 
at  equal  distances  around 
the  circumference  of  the 
hearth,  and  through  which 
a  constant  supply  of 
broken  carbon  is  fed. 

The  raw  sulphur  is  made  to  perform  a  primary  duty  before 
finally  entering  into  combination  with  the  carbon.  It  is 
fed  in  cold,  through  hoppers  H  H,  which  convey  it  into 
annular  chambers,  entirely  surrounding  the  furnace  body 
and  hearth :  in  these,  the  sulphur,  whilst  still  in  a  cold  state, 
acts  as  a  heat-conserving  jacket,  and  only  becomes  molten 
when  it  approaches  the  bottom  of  the  annular  chambers, 
which  communicate  with  the  furnace  hearth,  and  through 
which  the  sulphur  feed  is  effected.  It  thus  reaches  the 
centre  of  activity  in  a  heated  condition,  and  no  undue 
lowering  of  the  general  temperature  results. 

56 


Fid.  13. 


THEIR    INDUSTRIAL   APPLICATIONS 

By  varying  the  electrical  connexions  to  the  four  terminal 
hoppers,  a  very  thorough  and  complete  fusion  of  the  carbon 
and  sulphur  is  effected  in  the  region  of  the  hearth. 

The  dimensions  of  these  furnaces,  as  used  at  Penn  Yan, 
are :  height,  41  feet ;  diameter,  16  feet ;  and  they  require 
a  current  of  4,000  amperes,  at  from  40  to  60  volts,  to  operate 
them.  The  regulation  is,  to  a  certain  extent,  automatic  ; 
as  the  temperature,  and  consequently  the  degree  of  fusion, 
increases,  more  molten  sulphur  flows  in  to  the  bottom  of  the 
hearth  from  the  sulphur  jackets,  and  the  level  of  the  molten 
mass  rises  until  it  encircles  the  electrode  hoppers,  and  gives 
rise  to  an  increase  in  the  electrical  resistance  of  the  active 
column,  with  a  consequent  decrease  in  the  current  until  the 
working  conditions  again  become  normal. 

A  later  modification  consists  in  locating  the  active  heat 
zone  nearer  to  the  furnace  base,  a  procedure  which  renders 
it  possible  to  tap  off  accumulations  of  slag  resulting  from 
impurities  in  the  charge. 

Early  experiments  in  1903  showed  an  output  of  5,000 
kgs.  of  carbon  bisulphide  per  furnace  in  24  hours,  but  this 
figure  has  since  been  considerably  increased.  The  output 
from  the  Penn  Yan  furnaces,  to  June  1902,  was  1,500  tons. 

The  carbon  bisulphide  furnaces  at  Penn  Yan  are  the 
largest  electric  furnaces  at  present  in  use. 


57 


ELECTRIC  FURNACES  AND 


SECTION    IV 

CALCIUM  CARBIDE  MANUFACTURE 

General. — Calcium  carbide,  expressed  in  chemical  formula, 
CaC2,  is  produced  by  heating  together  a  mixture  of  65  per 
cent,  lime,  with  35  per  cent,  carbon,  or  coke. 

A  very  high  temperature,  approximately  3,312°C.  = 
6,000°F.,  is  required  to  effect  the  combination,  the  oxygen 
of  the  lime  being  driven  off,  and  uniting  with  a  certain 
percentage  of  carbon,  to  form  monoxide  (CO)  and  dioxide 
(C02)  of  carbon.  Some  heat  is  necessarily  evolved  as  a 
result  of  the  chemical  combination  pure  and  simple,  but 
it  is  insufficient  to  render  the  mixture  self-heating  ;  con- 
sequently artificial  means,  in  the  shape  of  the  electric 
furnace,  have  to  be  resorted  to,  in  order  that  the  mass  may 
be  raised  to  the  requisite  temperature. 

As  early  as  1862,  Wohler  prepared  calcium  carbide,  by 
heating  an  alloy  of  zinc  and  calcium  in  the  presence  of  an 
excess  of  carbon,  but  failed  to  isolate  the  compound.  In 
1893,  Travers  also  succeeded  in  manufacturing  calcium 
carbide,  though  in  admixture  with  other  substances,  by 
heating  a  mixture  of  calcium  chloride,  carbon,  and  sodium. 
jr;  Moissan,  however,  must  be  credited  with  having  been  the 
first  to  manufacture  and  isolate  calcium  carbide  with  the  aid 
of  the  electric  furnace.  He  published  his  discovery  on 
December  12,  1892,  in  the  form  of  a  paper  communicated 
to  the  Academie  des  Sciences,  which  ran  thus— 

"  If  the  temperature  (in  the  electric  furnace)  reaches 
3,000°C.  —  5,432°F.,  the  lime  forming  the  furnace  melts 

58 


THEIR   INDUSTRIAL   APPLICATIONS 

and  runs  like  water.  At  this  temperature  carbon  quickly 
reduces  calcium  oxide,  and  the  metal  is  separated  in  quantity ; 
it  unites  easily  with  the  carbon  of  the  electrodes  to  form  a 
carbide  of  calcium,  liquid  at  a  red  heat,  and  easily  collected." 

At  the  end  of  1892  Willson  announced  his  discovery  of 
calcium  carbide,  which  had  been  made  independently,  and 
apparently  without  knowledge  of  Moissan's  researches  on 
the  subject.  Thos.  L.  Willson,  the  original  discoverer  of  a 
commercial  process  of  calcium  carbide  manufacture,  was,  in 
1885,  an  employe  of  the  Brush  Company  at  Cleveland, 
where  the  Cowles  Bros,  were  then  operating  their  electric 
furnace.  He  subsequently  experimented  with  the  electric 
furnace  at  Spray,  N.C.,  U.S.A.,  where  the  first  successful 
production  of  calcium  carbide  was  effected  in  1888. 

His  attempts  to  patent  its  methods  of  production  in  the 
electric  furnace  proved  futile,  and  the  only  patents  now 
standing,  which  bear  on  carbide  manufacture,  either  relate 
to  certain  details  in  the  design  of  the  furnaces  themselves, 
or  to  such  subsidiary  processes  as  tend  to  promote  the 
efficiency  of  manufacture,  e.g.  the  preheating  of  the  raw 
materials  by  suitable  combustion  of  the  reaction  gases. 

With  reference  to  the  early  history  of  calcium  carbide, 
Vivian  B.  Lewes,  Acetylene,  tells  us  that  in  1886-1887  the 
lads  employed  at  the  Cowles'  aluminium  works  were  actually 
playing  with  the  substance,  and  experimenting  with  the 
acetylene  gas  evolved  on  bringing  it  into  contact  with  water. 
Yet  it  was  not  until  1892,  five  years  later,  when  its  commercial 
value  and  mode  of  preparation  had  been  independently 
studied  by  Willson  and  Moissan,  that  it  became  an  industrial 
product. 

In  France,  M.  Louis  Michel  Bullier  claims  to  be  the 
orignal  discoverer  of  crystalline  calcium  carbide,  and  his 
claims  have  been  upheld  by  the  French  Courts.  The 
Bullier  patents  belong  to  the  Societe  des  Carbures  Metal- 
liques,  a  Parisian  company  founded  by  Bullier.  In  1903, 
this  concern,  which  controls  the  output  of  17  carbide  fac- 

59 


ELECTRIC   FURNACES   AND 

tories  in  the  Alpine  districts,  compelled  its  dealers  to  sell 
at  a  uniform  price  of  £14  per  metric  ton.  The  annual  out- 
put is  estimated  at  18,000  tons. 

Commercial  calcium  carbide,  in  which  iron  is  usually 
present  as  an  impurity,  is  a  grey  mass,  with  a  metallic 
appearance  and  a  crystalline  fracture.  Its  specific  gravity 
is  2*22,  and  its  crystals,  examined  under  the  microscope, 
are  seen  to  be  transparent,  and  of  a  reddish  tint,  due  to  the 
impurities  present. 

When  brought  into  contact  with  water,  calcium  carbide 
decomposes  rapidly  into  lime,  and  acetylene  gas,  which 
latter  is  given  off.  The  equation — 

CaC2  +2H20  =  Ca  (OH)2  +C2H2, 

represents  the  reaction  which  takes  place.  Acetylene  has 
also  been  produced  directly  in  the  arc  furnace  by  Berthelot, 
who  succeeded  in  bringing  about  the  direct  union  of  carbon 
and  hydrogen  in  the  requisite  proportions. 

M.  Gin  has  made  an  extensive  study  of  the  reactions  which 
take  place  in  a  carbide  furnace  during  the  formation  of 
calcium  carbide.  Regarding  the  furnace  contents  as  a 
series  of  layers,  in  which  the  temperature  rapidly  decreases 
from  the  interior  to  the  exterior,  he  finds  that,  in  these 
layers,  different  chemical  equilibria  are  formed,  the  reaction 
being  more  endothermic  the  higher  the  temperature.  The 
gases  evolved  in  different  parts  of  the  furnace  contain  both 
free  oxygen  and  free  calcium.  The  former  is  liberated 
at  the  points  of  maximum  temperature,  or,  in  other  words, 
its  quantity  increases  with  the  current  density.  Calcium 
vapours,  on  the  other  hand,  originate  at  points  of  lower 
temperature.  The  presence  of  free  oxygen  sets  up  combus- 
tion of  the  electrodes,  immediately  below  the  surface  of 
the  charge,  whilst  the  calcium  is  deposited  as  the  fine  dust 
so  familiar  to  carbide  workers. 

Gin  explains  the  presence  of  these  two  elements  in  a  free 
state,  by  referring  to  the  researches  of  Berthelot,  who  proved 

60 


THEIR    INDUSTRIAL    APPLICATIONS 

that  carbon  monoxide  is  dissociated  at  high  temperatures  ; 
in  the  majority  of  commercial  formulae  for  carbide  furnace 
charges  there  is  an  excess  of  lime.  The  formation  of 
calcium  carbide  consists  in  simple  substitution  of  carbon  for 
the  oxygen  of  the  latter.  The  carbon  monoxide  formed 
as  a  secondary  product  of  the  reaction  is,  in  the  hottest 
parts  of  the  furnace,  entirely  dissociated,  whilst  calcium 
vapours  are  evolved  at  the  boundary  surfaces  of  calcium 
oxide,  and  calcium  carbide. 

In  a  resistance  furnace,  calcium  carbide  commences  to 
form  at  a  current  density  of  1*2  amperes  per  square  milli- 
metre, through  the  core,  whilst,  if  the  density  be  increased 
to  2  amperes  per  square  m.m.,  the  product  assumes  a  fluid 
condition.  According  to  Vogel,  at  the  latter  density  in 
the  core  of  a  resistance  furnace,  fluid  calcium  carbide 
commences  to  form  rapidly  in  the  immediate  neighbourhood 
of  the  core.  This  rapid  formation,  however,  only  extends 
over  a  region  of  some  three  or  four  centimetres  from  the 
core,  the  remainder  of  the  charge,  though  incandescent, 
remaining  in  a  semi-solid  condition,  in  which  state  it  forms 
a  gradually  increasing  mass,  disposed  in  shunt  to  the  resist- 
ance core  proper,  conducting  a  considerable  portion  of  the 
main  current  through  itself,  and  thereby  decreasing  the 
heating  efficiency  of  the  core. 

The  result  is  a  mixture  of  true  carbide,  with  a  partially 
converted  remainder,  which  offers  difficulties  in  the  way  of 
economical  separation.  It  is  therefore  necessary,  in  the 
operation  of  carbide  furnaces  of  this  description  with  a  single 
core,  that  the  furnace  charge  be  periodically  broken 
up,  or  agitated,  and  the  crust  formation  thereby  pre- 
vented. 

To  obviate  this  defect,  it  has  been  suggested,  and,  in 
fact,  a  German  patent  (No.  120,831,  February  8,  1900)  has 
been  taken  out  on  a  resistance  carbide  furnace,  of  which 
the  core,  in  multiple,  is  disposed  in  the  form  of  a  gridiron, 
which  effectually  prevents  the  formation  of  a  superimposed 

61 


ELECTRIC    FURNACES    AND 

and  uneconomical  crust,  whilst  the  carbide  formed  falls 
away,  by  virtue  of  its  own  weight,  to  the  hearth  of  the 
furnace,  the  raw  materials  descending  from  above  to  take 
its  place. 

Of  such  a  gridiron  formation  of  five  electrodes,  100  m.m. 
deep,  15  m.m.  thick,  and  1,200  m.m.  long,  the  total  weight 
is  13' 5  kgs.  ;  the  cross-sectional  area,  7,500  square  m.m.  ; 
and  the  electrical  resistance,  0*003  ohms.  The  current 
required,  at  a  density  of  2  amperes  per  square  m.m.,  is 
15,000  amperes,  at  a  pressure  of  45  volts,  or  1,100  (German) 
H.P.,  of  which  920  are  utilized  in  the  furnace.  This  disposi- 
tion is  secured  by  arranging  three  furnaces  in  series,  the 
1,200  m.m.  of  resistance  core  length,  being  equally  divided 
between  them.  In  the  three  furnaces,  with  gridiron  cores, 
proportioned  as  above,  there  would  be  a  total  effective 
heating  surface  of  13,800  square  c.m.,  as  compared  with 
675  square  c.m.  in  a  three-electrode  arc  furnace  with  square 
carbons,  each  of  150  m.m.  side. 

Assuming  a  yield  of  0'2  kg.  of  carbide  per  H.P.  hour,  the 
expenditure  of  900  H.P.  would  produce  180  kgs.  per  hour 
in  each  furnace,  or  a  total  of  540  kgs. 

MM.  Vulitch  and  d'Orlowsky,  of  Paris,  suggest  the  pre- 
paration of  calcium  carbide  by  first  fusing  the  lime,  per  se, 
in  an  arc  furnace,  and  then  pouring  it  into  an  excess  of  some 
heavy  hydrocarbon,  such  as  the  residue  from  petroleum 
distillation,  in  the  body  of  which  the  actual  carbide  forma- 
tion takes  place.  The  product  is  loose  and  non-coherent, 
and  saturated  throughout  with  the  hydrocarbon,  which 
renders  it  practically  non-hygroscopic  and  adapted  for  the 
intermittent  generation  of  acetylene,  evolution  of  the  latter 
only  taking  place  during  actual  immersion  in  water. 

In  the  manufacture  of  calcium  carbide,  as  in  other  electric 
furnace  processes,  the  tendency  has  been  to  revert  to  the 
more  moderate  and  easily  regulable  "  resistance  "  principle 
of  working.  It  is,  however,  questionable  whether  calcium 
carbide  has  ever  been  manufactured,  commercially,  without 

62 


THEIR    INDUSTRIAL   APPLICATIONS 

the  development  of  an  arc  or  arcs,   within  the  mass  of    ! 
material  bridging  the  electrodes. 

As  M.  Pradon  points  out,  the  presence  of  vapours  of 
calcium  and  carbon  in  the  neighbourhood  of  the  electrodes 
reduces  the  E.M.P.  necessary  for  the  striking  of  an  arc  to 
from  8-10  volts,  a  pressure  at  which,  owing  to  the  imprac- 
ticable increase  in  cross-sectional  area  of  the  furnace  elec- 
trodes and  connexions,  it  would  be  impossible  to  operate. 

It  is,  of  course,  possible  to  smother  the  arc  by  judicious 
feeding  of  the  raw  materials,  but  the  constantly  changing 
nature  and  irregular  movement  of  the  charge  permit  it  to 
strike  again. 

Bearing  these  facts  in  mind,  it  would  seem  probable  that 
the  whole  commercial  process  of  carbide  manufacture 
depends  upon  a  combination  of  the  arc  and  resistance 
principles  of  furnace  working,  which  operate  irregularly, 
and  irrespective  of  the  design  of  the  furnace  itself,  in  so  far 
as  the  latter  may  be  intended  to  confine  the  reaction  to  one 
or  the  other  of  the  two  principles  of  operation. 

The  calcium  carbide  of  commerce  cannot  be  purified  by 
any  of  the  usual  methods  adopted  with  fusible  and  soluble 
products,  in  that  it  is,  to  all  practical  intents  and  purposes, 
infusible,  and  insoluble  in  any  known  solvent.  It  remains, 
therefore,  to  produce  the  carbide  in  as  pure  a  state  as  possible, 
such  that  subsequent  purification  is  rendered  unnecessary. 

There  are,  at  present,  two  known  methods  of  achieving 
this  result,  both  of  which  consist  in  the  addition  of  foreign 
materials  to  the  charge  of  carbon  and  lime  undergoing 
treatment  in  the  furnace,  which,  either  by  combination 
with  the  impurities,  or  reacting  upon  them  during  the  pro- 
cess, render  them  innocuous  or  convert  them  into  such  a 
form  as  permits  of  their  ready  removal  from  the  finished 
product. 

Hewes'  method  consists  in  employing,  as  a  furnace  charge, 
a  mixture  of  26  parts  carbon,  64  lime,  8  calcium  carbonate, 
and  2  peroxide  of  manganese.  The  function  of  the  latter 

63 


ELECTRIC    FURNACES   AND 

is  to  form  carbide  of  manganese  (MnC3),  which  reduces  the 
temperature  of  the  reaction,  and  tends  to  increased  fluidity 
of  the  product.  Methane  (CH4)  is  also  produced,  and  serves 
as  a  diluent,  lessening  the  tendency  to  a  sooty  deposit  from 
the  acetylene  subsequently  produced  from  the  carbide. 

The  object  of  adding  calcium  carbonate  to  the  mixture 
is  to  produce  a  generous  yield  of  gas,  which,  bubbling  up 
through  the  carbide,  carries  with  it  such  impurities  as  the 
sulphides  and  phosphides  of  calcium  to  the  surface,  leaving 
them  there  in  the  form  of  a  crust,  which  is  readily  separated 
from  the  charge  when  the  furnace  is  opened. 

Dr.  W.  Rathenau's  process  is  specially  adapted  to  the 
getting  rid  of  silicious  impurities  in  either  the  lime  or  carbon. 
He  adds  to  the  charge  a  metal,  preferably  iron,  or  its  oxide, 
in  sufficient  quantity  to  take  up  and  combine  with  all  the 
silicon  present  as  impurities.  The  result  is  the  formation 
of  iron  siticide,  which  collects  at  the  bottom  of  the  furnace 
below  the  carbide,  and  may  be  drawn  off,  or  subsequently 
separated  from  the  charge,  as  circumstances  may  deter- 
mine. 

Silicide  of  iron,  or  ferro-silicon,  thus  produced,  constitutes 
a  useful  by-product  and  may  be  marketed  for  various 
purposes. 

Temperature  of  Formation. — There  has  been  considerable 
discussion  as  to  the  temperature  of  formation  of  calcium 
carbide.  Several  experimenters  have  tackled  the  subject 
with  a  view  to  ascertaining  the  exact  degree  of  heat  neces- 
sary ;  among  others,  Rothmund  and  Borchers  (Zeitschrift 
fur  Elektrochemie,  May  29,  1902).  The  former  proved,  by 
experiment,  that  the  lowest  temperature  at  which  calcium 
carbide  can  be  formed  is  1,620°C.  =  2,948°F.  Below  this 
temperature,  again,  at  1,560°C.=  2,840°F.;  and  in  the 
presence  of  carbon  monoxide  gas,  the  carbide  already  formed 
is  disintegrated,  or  split  up,  into  its  constituent  elements. 

Borchers,  who  conducted  his  experiments  with  the  aid 
of  blow-pipe  heating,  found  that  a  temperature  of  approxi- 


THEIR   INDUSTRIAL   APPLICATIONS 

mately2,000°C.  =  3,632°F.,was  necessary  for  the  formation 
of  crystalline  calcium  carbide,  from  which  it  will  be  seen 
that  although,  theoretically,  only  1,620°C.  is  necessary,  a 
temperature  of  at  least  2,000°C.  is  required  in  practice. 

Quality. — The  commercial  quality  of  calcium  carbide  is 
determined  by  its  capacity  for  evolving  acetylene  gas. 
One  kilogramme  of  pure  calcium  carbide  evolves  348' 4  litres 
of  acetylene,  the  latter  being  determined  at  a  pressure  of 
760  m.m.,  and  a  temperature  of  0°C.  =  32°F.  This  is 
equivalent  to  5' 587  cubic  feet  of  gas  per  pound  of  carbide. 
The  calcium  carbide  of  commerce  seldom  yields  more  than 
300  litres  per  kg.,  the  average  figure  being  between  280  and 
290,  or  86  per  cent. 

Current  Used  in  Calcium  Carbide  Manufacture. — Either 
continuous  or  alternating  current  may  be  used  in  the  pro- 
duction of  calcium  carbide,  and  an  alternating  plant  is, 
in  many  cases,  preferable,  in  that  it  lends  itself  more  readily 
to  long  distance  transmission,  and  is,  withal,  better  capable 
of  withstanding  the  strains  incidental  to  large  variations 
in  the  load,  such  as  are  invariably  encountered  in  electric 
furnace  working. 

An  interesting  article  by  M.  J.  Pradon,  in  the  Zeitschrift 
fur  Calciumcarbid  Fabrication,  1901,  entitled  "  The  In- 
fluence of  the  Nature  of  the  Electric  Current  on  the  Manu- 
facture of  Calcium  Carbide,"  throws  some  interesting 
light  on  many  debatable  points  connected  with  this  exten- 
sive application  of  electric  furnace  methods. 

Discussing  the  probability  of  electrolytic  action  taking 
place  in  a  carbide  furnace  when  continuous  currents  are 
employed,  M.  Pradon  discounts  the  greatly  magnified 
drawbacks  incidental  to  continuous  current  working.  He 
states,  however,  that,  under  exactly  similar  conditions,  and 
given  identical  charges  of  raw  material,  the  carbide  pro- 
duced in  a  continuous  current  furnace  is  of  a  lower  gas- 
producing  quality  than  that  resulting  from  the  action  of  an 
alternating  current ;  the  former  product  is  of  a  compact 

65  F 


ELECTRIC   FURNACES   AND 

nature,  which  offers  considerable  resistance  to  fracture, 
whilst  the  latter  is  crystalline,  and  breaks  readily. 

Another  interesting  fact  which  has  been  noted  in  connexion 
with  the  operation  of  both  types  of  furnace  is,  that  in  the 
case  of  direct  current  it  is  necessary  that  the  preliminary 
mixing  of  the  charge  be  thorough,  in  order  to  ensure  homo- 
geneity, whereas,  with  an  alternating  current  furnace,  a 
very  casual  mingling  of  the  constituents  suffices. 

In  connexion  with  the  use  of  alternating  currents  for 
carbide  furnace  work,  M.  Pradon  lays  considerable  stress 
on  the  lag  due  to  self-induction,  and,  to  obviate  losses  from 
this  cause,  he  has  designed  a  furnace  operating  on  the  "  con- 
centric "  principle. 

It  consists  of  a  movable  hearth,  in  the  form  of  a  truck 
mounted  on  wheels,  which  receives  and  retains  the  carbide 
formed,  and  can  be  removed  and  replaced  when  full.  When 
placed  in  position  in  the  furnace,  this  truck  is  located  below 
the  centre  of  a  metal  chimney  or  flue,  which  serves  to  conduct 
away  the  gases  of  combustion.  Down  the  centre  of  this 
chimney  passes  the  vertical  electrode.  The  side  walls  of 
the  furnace  are  of  metal,  and  one  connexion  from  the  alter- 
nating current  generator  is  made  to  the  upper  portion  of 
these  walls,  whilst  the  other  is  made  to  the  lower  extremity 
of  the  chimney. 

The  path  taken  by  the  current  is  thus  downward  through 
the  metallic  walls  of  the  furnace,  into  the  truck  or  hearth, 
and  up  through  the^  unconverted  mixture  therein  to  the 
vertical  electrode,  through  which  it  passes  to  the  upper 
extremity  of  the  chimney,  and  down  again,  being  thus, 
through  every  portion  of  its  circuit,  subjected  to  the  neutral- 
izing effect  of  a  return  current. 

An  alternative  method  for  the  elimination  of  self-induction 
losses  in  an  alternating  current  furnace  is  to  do  away  with 
the  arc  and  effect  the  conversion  on  the  "  resistance " 
principle.  According  to  M.  Pradon,  this  plan  is  impractic- 
able, as,  owing  to  the  presence  of  vapours  of  calcium  and 

66 


THEIR    INDUSTRIAL    APPLICATIONS 

carbon,  an  arc  is  struck  at  a  very  low  voltage,  even  8  to  10 
volts  being  sufficient.  To  operate  below  this  voltage  would 
entail  an  impracticable  increase  in  the  cross-sectional  area 
of  the  furnace  electrodes  and  connexions  thereto. 

Raw  Materials. — As  regards  the  raw  materials  used  in 
calcium  carbide  manufacture,  certain  advantages,  such  as 
freedom  from  ash,  and  consequent  contamination  of  the 
carbide  with  silicon,  magnesium,  iron,  and  similar  impurities, 
are  claimed  for  the  carbon  resulting  from  woody  tissue, 
which  is  utilized,  notably  in  the  three-phase  Memmo 
furnaces,  to  be  described  later. 

In  this  connexion,  a  brief  allusion  to  Prof.  V.  L.  Emerson's 
invention  for  the  conversion  of  saw-dust  and  saw-mill 
refuse  into  commercial  products  including  a  special  form 
of  carbon  for  carbide  manufacture,  may  prove  of  interest. 

The  saw-dust,  having  first  been  subjected  to  a  drying 
process,  which  is  effected  by  the  combustion  gases  derived 
from  its  subsequent  treatment,  is  next  charged  into  a  retort 
consisting  of  a  vertical  iron  cylinder,  some  15  to  20  ft. 
high,  by  3  ft.  in  diameter,  surrounded  by  brickwork. 

Within  the  cylinder  are  a  series  of  perforated  hoods, 
mounted  on  a  central,  hollow,  revolving  shaft,  which  is  also 
provided  with  perforations  between  the  hoods.  The 
gaseous  products  from  the  distillation  process  which  is 
carried  on  in  this  apparatus  make  their  way  out  at  the  lower 
end  of  the  cylinder,  and,  having  passed  through  a  purifying 
process,  are  partly  used  in  carbonizing  the  charge  by  being 
forced  through  it  as  it  passes  down  the  retort,  and,  for  the 
rest,  serve  to  dry  the  sawdust,  as  already  stated.  The 
liquid  products  of  the  distillation  are  also  collected  and 
separated,  being  subsequently  drawn  off  through  two  out- 
lets ;  of  these,  one  is  a  wood  creosote  product  which  can  be 
utilized  for  a  variety  of  purposes,  and  the  other,  crude 
pyroligneous  acid,  from  which  wood  alcohol,  acetic  acid, 
and  various  other  products  can  be  prepared.  The  carbon 
remainder  passes  out  through  a  separate  opening,  and  is 


ELECTRIC   FURNACES   AND 

said  to  be  a  very  pure  form  of  carbon,  especially  adapted 
for  carbide  manufacture. 

Experience  has  demonstrated  that  a  carbide  furnace 
works  at  its  best  when  fed  with  a  raw  mixture  of  carbon 
and  lime  which  has  been  reduced  to  granular  form  rather 
than  powdered.  Extreme  comminution  of  the  charge  is 
inadvisable  in  that,  setting  aside  the  principal  question  of 
the  expense  involved  in  thus  reducing  the  ingredients  to  a 
powder,  there  remains  the  additional  disadvantage  that, 
when  thus  finely  divided,  they  agglomerate  round  the 
electrodes,  forming  an  impermeable  coating,  which  hinders 
the  free  escape  of  the  gases  formed  in  the  reaction. 

The  action  which  takes  place  in  a  carbide  furnace  in  the 
immediate  neighbourhood  of  the  electrodes,  when  fed  with 
a  charge  which  has  been  too  finely  divided,  is  thus  described 
by  Berger  Carlson,  in  an  article  which  appeared  in  Zeit- 
schrift  fur  Elektrochemie,  about  the  end  of  1899. 

Carbon  monoxide  gas  is  formed  as  a  natural  result  of  the 
reaction,  and  by  reason  of  the  impermeability  of  the  finely 
powdered  charge,  forms  a  cavity  round  the  electrodes,  the 
inner  walls  of  which,  from  exposure  to  the  radiant  heat  of 
the  arc,  become  glazed  by  the  fusion  of  the  lime  and  its 
subsequent  reaction  upon  the  particles  of  carbon  in  its 
immediate  neighbourhood.  The  internally  glazed  cavity 
thus  formed  still  further  encloses  the  reaction  gases,  with 
the  result  that  the  pressure  gradually  rises,  until  the  walls 
of  the  cavit}^  give  way,  and  allow  a  portion  of  the  carbon 
monoxide  to  escape,  carrying  with  it  a  portion  of  the  charge 
in  the  form  of  dust.  Channels  are  thus  formed  within  the 
general  mass  of  the  charge  and,  by  virtue  of  the  highly 
heated  carbon  monoxide  from  the  region  of  the  arc  passing 
through  them,  also  become  glazed,  and  serve  to  conduct 
away  from  the  furnace  a  considerable  quantity  of  heat  which 
would  otherwise  serve  a  useful  purpose. 

This  constant  honeycombing  of  the  mass  of  raw  material 
and  subsequent  caving  in  of  the  recesses  formed  gives  rise 

68 


THEIR    INDUSTRIAL    APPLICATIONS 

to  serious  fluctuations  in  the  load,  by  setting  up  constant 
changes,  having  a  considerable  range,  in  the  resistance  of 
the  fused  mass  which  bridges  the  electrodes. 

In  order  to  eliminate  these  various  drawbacks,  the  same 
authority  advocates  the  use  of  a  mixed  charge,  the  particles 
of  which  have  been  reduced  to  the  size  of  hazel  nuts,  and 
quotes  statistics  which  go  to  prove  that,  whereas,  with  a 
finely  powdered  charge,  3,000  kgs.  are  necessary  for  the 
production  of  1,000  kgs.  of  carbide,  only  1,700  kgs.  are 
required  for  the  production  of  a  similar  quantity  when  the 
charge  is  of  a  coarse  or  granular  nature. 

It  may  be  mentioned  that  the  quantity  of  raw  material 
theoretically  required  for  the  manufacture  of  1,000  kgs.  of 
calcium  carbide,  is  1,440  kgs. 

Furnaces. — The  improvement  of  electric  furnaces  for 
the  production  of  calcium  carbide,  judging  from  the  number 
of  applications  for  patents,  seems  to  have  been  a  favourite 
theme  for  inventors.  Thus,  according  to  Kershaw  (Electrical 
Review,  July  7,  1899),  the  number  of  applications  for  patents 
on  inventions  for  the  production  and  utilization  of  calcium 
carbide  numbered,  in  1896,  159  ;  in  1897,  172  ;  and  in  1898, 
124. 

Many  of  the  furnace  constructions  dealt  with  are  most 
ingenious,  the  principal  aim  on  the  part  of  the  designers 
being,  apparently,  continuity  of  furnace  action,  whereby 
the  plant  may  be  worked  continuously,  day  and  night, 
with  a  consequent  gain  in  efficiency  ;  and  auxiliary  heating 
devices,  whereby  the  raw  material  is  heated  to  a  certain 
extent,  prior  to  its  introduction  into  the  furnace,  thereby 
involving  a  lesser  expenditure  of  electrical  energy  than 
would  otherwise  be  necessary  for  a  given  output  of  carbide. 

Blount,  in  his  paper  before  the  Manchester  Section  of 
the  Institution  of  Electrical  Engineers,  suggests  a  suitable 
design  for  a  carbide  furnace,  based  on  the  following  re- 
quirements— 

1.  The  furnace  should  make  carbide  sufficiently  fluid  to 

69 


ELECTRIC    FURNACES    AND 


be  tapped  and  run  away  from  the  sphere  of  action ;  i.e.  it 
must  be  continuous  in  operation. 

2.  It  should  not    have  an  exposed  arc,   and    the  heat 
electrically   generated    should    be    conserved    as    much    as 
possible. 

3.  It  should  be  so  constructed  that  the  containing  vessel 
is  hardly  affected  by  the  high  temperature  necessary  to 
form  carbide. 

Basing  his  design  upon  the  three  conditions  set  forth 

above,  Blount  suggests  the 
furnace  construction  illus- 
trated in  Fig.  14.  The  fol- 
lowing is  his  own  description 
of  the  apparatus,  which  would 
certainly  appear  to  possess 
several  advantages  over  exist- 
ing types. 

"  The  furnace  consists  of  a 
fire-brick  casing  A,  with  a 
magnesia  lining  B .  The  shape 
is  conical,  and  at  the  bottom 
the  furnace  is  contracted  to 
form  a  hearth  for  the  fused 
carbide.  The  tapping  hole  is 
at  the  bottom  of  this  con- 
tracted part.  The  lower  elec- 
trode is  a  carbon  plate  C,  and  the  upper  electrode,  a  massive 
carbon  rod  D,  of  circular  section. 

"  The  raw  material  is  fed  into  the  annular  space  between 
the  upper  electrode  and  the  magnesia  lining  in  sufficient 
quantity  to  enclose  and  smother  the  zone  of  highest  tem- 
perature. This  feeding  may  be  done  mechanically,  and 
various  devices  suggest  themselves,  but  it  is  probable  that 
hand-feeding  will  be  at  least  as  effective,  because  the 
amount  of  labour  required  is  not  great,  and  the  variation 
of  conditions  is  so  large,  that  the  greater  elasticity  of  hand- 

70 


FIG.  14. 


THEIR    INDUSTRIAL   APPLICATIONS    \ 

feeding  may  be  a  positive  advantage.  For  the  safety  of 
the  workmen  it  may  be  necessary  to  draw  off  the  carbon 
monoxide  by  a  fan  through  a  side  flue,  leaving  the  top  of 
the  furnace  open  and  uninterrupted  for  manipulating  the 
charge.  In  operating  the  furnace,  a  pool  of  carbide  will 
be  formed  and  maintained  of  such  depth  as  to  cover  the 
hearth  and  to  allow  of  tapping  the  pure  and  fairly  fluid 
product,  but  the  depth  of  this  pool  will  be  kept  small,  and 
special  attention  will  be  directed  to  maintaining  its  fluidity 
by  the  means  indicated  below.  It  will  be  observed  that 
the  cross-section  of  that  part  of  the  furnace  immediately 
surrounding  the  lower  end  of  the  upper  electrode  is  con- 
siderably greater  than  the  cross-section  of  the  hearth  on 
which  the  carbide  collects.  Thus  the  smaller  section  of 
the  column  of  carbide  compensates  for  its  conductivity 
being  greater  than  that  of  the  raw  materials  ;  the  desired 
temperature  can  be  maintained,  and  the  carbide  will  re- 
main sufficiently  fluid  to  be  tapped." 

Three-phase  furnaces,  as  employed  at  St.  Marcello 
d'Aosta,  enable  a  more  evenly  distributed  heating  effect 
to  be  obtained,  whilst,  in  practice,  it  has  been  found  that 
the  highest  output  of  carbide  is  obtained  from  the  inter- 
mittent type  of  furnace. 

Kicardo  Memmo,  commenting  on  calcium  carbide  manu- 
facture in  Italy,  sets  down  the  following  conditions  as 
essential  to  the  commercial  success  of  the  industry — 

1.  The   price   of   the   plant,  per   horse   power   installed, 
including  machinery,  furnaces,  and  all  the  necessary  supplies, 
must  not  be  higher  than  500  francs  =£20  approximately. 

2.  A  certain  ratio  between  the  number  of  tons  produced, 
and  the  number  of  effective  H.P.  produced,  must  exist.    The 
price  of  calcium  carbide,  including  general  expenses,  must 
not  be  more  than  120  francs  =£4  15s.  per  ton. 

3.  The  capital  expended  must  be  liquidated  in  ten  years. 
This  corresponds  to  a  sinking  fund  of  40  francs  =£1   12s. 
per  ton  produced. 

71 


ELECTRIC    FURNACES    AND 


4.  The  selling  price  of  the  carbide  must  be  250  francs 

=£10  per  ton,  so  that,  including  freight,  loss,  profits,  etc., 

the  price  to  consumer  must  not  exceed  300  francs  =£12 

per  ton.     On  the   capital  invested,   at  least   6  per   cent. 

must  be  paid. 

The  Willson  carbide  furnace,  as  originally  constructed, 
is  represented  in  Fig.  15,  and  consists  of  an  outer  struc- 
ture F  of  fire-brick,  with  a  lining  of  carbon  C,  which 

constitutes  the  crucible,  or 
hearth  of  the  furnace,  and 
was  covered  in  by  a  lid  L, 
also  of  carbon,  through  the 
centre  of  which  passed  the 
upper  carbon  electrode  E, 
adjustment  being  effected  by 
means  of  a  hand-wheel  W 
and  screwed  rod  R,  attached 
to  the  clamp  D  supporting 
the  carbon.  T  is  a  tapping 
hole,  for  drawing  off  the  car- 
bide formed,  in  a  molten 
state.  Incidentally,  it  may 
be  recorded  that  this  furnace 
was  not  originally  designed 
FIG.  15.  for  carbide  manufacture,  but 

was  intended  for  the  reduc- 
tion of  aluminium,  and  was  found  unsuitable  for  the  pur- 
pose. 

The  charge  was  introduced  in  small  quantities  at  a  time, 
the  electrode  E  being  gradually  raised,  meanwhile,  until 
a  layer  of  molten  carbide  was  produced  at  the  bottom  of 
the  carbon  crucible  C,  which  then  took  the  place  of  the 
second  electrode. 

This  was  followed  by  an  improved  form  of  the  Willson 
furnace,  in  which  a  removable  truck,  mounted  on  wheels, 
took  the  place  of  the  fixed  carbon-lined  crucible,  and  was 

72 


THEIR    INDUSTRIAL    APPLICATIONS 

provided  with  a  massive  cast-iron  base,  which  serves  as 
the  second  electrode.  This  modified  furnace  was  not 
hermetically  sealed,  the  whole  of  one  side  being  merely 
closed  by  iron  doors  whilst  the  furnace  was  in  action.  The 
free  circulation  of  air  possible  with  this  design  led  to  con- 
siderable loss  and  trouble,  arising  out  of  the  waste  of 
material  and  rapid  consumption  of  the  upper  electrode  ; 
it  was,  therefore,  still  further  improved,  prior  to  its  adoption 
for  carbide  manufacture  at  Foyers.  To  this  end  two  sides 
of  the  truck  hearth  were  made  removable,  and  consisted 
of  massive  cast-iron  bars,  each  provided  with  a  central 
opening  for  the  escape  of  the  carbon  monoxide  gas.  This 
horizontal  diffusion  of  the  gases  produced  in  the  reaction 
was  found  to  be  an  improvement  upon  the  more  usual 
vertical  arrangement. 

The  writer  understands  that  even  this  third  stage  in 
the  development  of  the  original  Willson  furnace  has  not 
proved  altogether  satisfactory  to  the  British  Aluminium 
Company  who  control  the  manufacture  of  calcium  carbide 
at  Foyers,  and  that  a  new  continuous  type  of  furnace, 
yielding  2,500  kgs.  of  80  per  cent,  carbide  per  1  E.H.P. 
year,  has  since  been  installed.  No  particulars  concerning 
this  later  furnace  are,  however,  available. 

The  Union  Carbide  Company,  of  Niagara,  U.S.A.,  owns 
and  works  the  Willson  furnace  patents  in  America.  It 
is  the  only  concern  manufacturing  calcium  carbide  in  the 
United  States,  and  its  capacity  is  in  process  of  extension 
to  100  tons  per  24  hours.  The  cost  of  manufacture  is 
stated  to  be  in  the  neighbourhood  of  £5  per  ton,  and  the 
product  is  graded  into  three  sizes,  varying  from  3J  in. 
to  2  in.,  2  in.  to  J  in.,  and  \  in.  to  ^  in.  respectively. 
Rotary  continuous  furnaces  are  employed,  and  the  dust  is 
worked  up  afresh  with  each  charge. 

The  Gin  and  Leleux  carbide  furnaces,  as  used  at  Meran, 
in  the  Austrian  Tyrol,  are  semi-intermittent  in  action, 
but  disposed  in  pairs,  and  furnished  with  an  ingenious 

73 


ELECTRIC   FURNACES   AND 

overhead  arrangement,  whereby  a  single  upper  electrode 
is  made  to  serve  for  either  furnace  in  turn.  By  thus 
working  one  furnace  whilst  the  other  is  cooling  and  being 
charged  afresh  with  raw  material,  a  practically  continuous 
operation  is  secured. 

In  general  principle,  the  furnace  resembles  the  modified 
Willson  type,  with  removable  truck  hearth.  There  is, 
however,  an  additional  feature  in  connexion  with  these 
furnaces  which  renders  their  mode  of  working  distinct 
from  that  of  the  Willson  type.  It  consists  in  a  revolving 
fan.  which  extracts  the  gases  produced  in  the  reaction 
from  the  furnace  chamber  by  suction,  and  passes  them  on 
to  be  utilized  in  a  preliminary  heating  of  the  next  charge  ; 
a  considerable  saving  in  the  upper  carbon  electrodes  is 
thereby  effected  as  the  gases  are  withdrawn,  or,  at  all 
events,  diluted  with  the  ingoing  air,  to  such  an  extent  that 
combustion  is  prevented. 

At  Meran  these  furnaces  have  each  a  capacity  of  260 
k.w.,  in  three  phases  of  2,500  amperes  at  33  volts.  Each 
furnace  operation  lasts  from  10  to  12  days  without  inter- 
mission, the  only  stoppages  necessary  being  for  the  replace- 
ment of  the  upper  electrode.  The  carbide  is  tapped  from 
the  furnaces  in  a  molten  condition,  through  two  orifices, 
or  nozzles,  so  designed  as  to  prevent  splashing.  When 
these  orifices  become  finally  choked,  as  they  do  after  several 
days,  the  remainder  of  the  operation  is  performed,  and 
the  furnace  filled,  by  raising  the  upper  electrode  until  the 
chamber  is  charged  to  its  utmost  capacity.  The  furnace 
is  then  cooled  and  opened,  and  the  block  of  carbide  formed 
removed. 

Five  kgs.  of  carbide  per  k.w.  day  of  24  hours  is  the 
output  claimed  for  these  furnaces. 

In  1900,  according  to  M.  Keller,  this  figure  had  been 
increased  to  6*2  kgs.  of  carbide  per  k.w.  day,  representing 
a  thermal  efficiency  of  about  75  per  cent. 

The  Gin  and  Leleux  furnaces  as  employed  at  Milan, 

74 


THEIR   INDUSTRIAL   APPLICATIONS 

Italy,  and  taking  their  energy  from  the  Paderno  three- 
phase  sub-station,  are  each  of  225  k.w.  capacity,  and  work 
at  a  terminal  E.M.F.  of  28-33  volts.  They  are  run  in  sets 
of  three,  star  connected,  one  in  each  leg,  or  phase,  of  the 
supply  system.  The  hearth  of  each  furnace,  which  is  in 
two  layers,  of  high  and  low  resistance  respectively,  con- 
stitutes one  electrode,  the  other  being  arranged  axially, 
and  capable  of  vertical  feed  adjustment. 

The  high  resistance  layer  of  the  hearth,  heated  by  the 
passage  of  the  current,  serves  to  maintain  the  carbide  in  a 
state  of  fusion. 

Graphite,  or  a  mixture  of  graphite  and  anthracite,  is  the 
substance  from  which  the  electrodes  are  manufactured,  and 
they  are  subjected  to  a  baking  heat  of  1,200°C.  =  2,192°F. 
for  ten  hours  before  use.  They  last  about  150  hours. 

Both  the  lime  and  coke  used  at  Milan  contain  at  least 
85  per  cent,  lime  and  carbon  respectively,  and  are  mixed, 
prior  to  being  fed  into  the  furnaces,  in  the  proportion  of 
64-68  parts  coke  to  100  lime.  The  resultant  carbide  is 
run  off  every  two  hours  in  quantities  varying  from  115- 
175  kgs.  for  each  furnace.  Each  run  lasts  80  hours,  the 
final  yield  being  from  1,100-1,350  kgs.  of  carbide. 

The  mean  yield  at  this  factory  in  1900  was  estimated  at 
5' 6  kgs.  per  k.w.  day. 

The  furnace  construction  devised  by  William  P.  Parks, 
of  Chicago,  was  based  upon  the  practicability  of  obtaining 
the  carbide  in  a  molten  state,  and  drawing  it  off  at  the 
base  of  the  furnace  as  formed,  thereby  rendering  the  pro- 
cess continuous. 

A  section  of  the  furnace,  as  originally  patented,  is  shown 
in  Fig.  16.  It  comprises  a  cylindrical  structure  F,  con- 
tracted half-way  down  as  shown  to  form  a  hearth,  which, 
in  the  shape  of  a  circular  block  of  carbon  C,  serves,  at  the 
same  time,  as  the  lower  fixed  electrode. 

In  the  upper  face  of  this  block,  which  is  flush  with  the 
contracted  portion  of  F,  an  annular  channel  c  is  cut,  and 

75 


ELECTRIC   FURNACES    AND 


led  into  a  tapping  opening  t,  its  object  being  to  collect  the 
molten  carbide  formed,  and  convey  it  out  of  the  furnace. 

The  upper  movable  electrode 
is  in  the  form  of  a  hollow 
carbon  cylinder  B,  its  lower 
extremity,  where  it  penetra/tes 
into  the  furnace,  being  sub- 
divided by  a  series  of  radial 
slots  as  shown  ats.  The  arc  is 
thus  split  up  into  a  number 
corresponding  with  the  number 
of  slots,  and  the  heating  effect 
thereby  distributed  throughout 
the  charge  instead  of  being  con- 
fined to  a  single  point,  as 
would  be  the  case  were  the 
extremity  of  the  electrode  left 
solid.  T  is  a  feeding  tube,  into 
which  the  raw  material  is  fed 
by  a  screw  conveyor  S  from  a 
feed  hopper  H,  and  passes 
down  the  centre  of  the  elec- 
trode B  into  the  zone  of 

greatest  activity.  In  passing  down  the  tubular  electrode  it 
receives  a  preliminary  heating  from  the  hydrocarbon  burners 
n  n,  which  are  introduced  through  the  side  walls  ;  a  con- 
siderable economy  in  the  current,  which  would  otherwise 
be  required  to  bring  the  charge  up  from  the  normal  tem- 
perature at  which  it  enters  the  hopper,  is  thereby  effected. 
The  resistance  furnace  for  the  manufacture  of  calcium 
carbide,  invented  by  Mr.  Hudson  Maxim,  is  of  an  inter- 
mittent type,  and  produces  the  carbide  in  "  block "  or 
"  ingot  "  form  instead  of  the  semi-molten  state  aimed  at 
by  many  inventors. 

It  consists  (Fig.  17)  of  a  rectangular,  refractory  chamber, 
R,   provided  with   means  for  the  introduction   and  with- 


FIG.   16. 


THEIR    INDUSTRIAL   APPLICATIONS 


drawal  of  the  truck  T,  which  constitutes  the  hearth  of  the 
furnace,  and,  running  on  rails,  is  easily  removed,  when  full 
of  carbide,  and  can  be  replaced  by  a  similar  empty  truck, 
without  any  serious  delay  in  the  process  of  manufacture. 
It  is  provided  with  a  refractory  lining,  B,  and,  through  per- 
forations in  one  of  its  side  walls  pass  a  series  of  horizontal 
pairs  of  electrodes,  E,  E2,  E3,  whilst  the  opposite  side  is 
slotted  to  permit  the  passage  of  the  plates  of  carbide,  p  p, 
which  serve  as  temporary  short-circuiting  pieces,  to  start 
the  action  of  the  furnace.  The  electrodes,  E,  E2,  etc., 
take  the  form  of 
hollow  carbon 
cylinders,  each 
mo unted  in  a 
metal  sleeve,  or 
combina t  i o n  of 
sleeves,  s,  the  in- 
tervening sp  a  c  e 
between  the  metal 
of  the  sleeve  and 
the  carbon  elec- 
trode, being  filled 
in  with  ground  car- 
bon to  ensure  good 

electrical  connexion.  Through  the  tubular  centre  of  the 
electrodes  a  supply  of  pulverized  carbon  is  fed  towards  the 
interior  of  the  furnace,  and  serves  to  protect  their  active 
extremities.  The  raw  material  is  fed  into  the  furnace 
through  the  central  opening  C,  its  rate  of  admission  being 
regulated  by  the  sliding  shutters  t  t,  whilst  a  preliminary 
heating  of  the  charge  is  secured  from  an  outer  flue,  kept  hot 
by  an  oxy-hydrogen  burner  b.  The  action  of  the  furnace 
is  started  by  short-circuiting  the  various  horizontal  pairs 
of  electrodes  by  means  of  the  plates  p  p  ;  once  started,  the 
action  is  maintained  through  the  carbide  of  the  charge 
itself,  and,  by  gradually  withdrawing  the  electrodes  E,  E2, 

77 


FIG.  17. 


ELECTRIC   FURNACES    AND 


etc.,  whilst  at  the  same  time  feeding  in  the  raw  material,  a 
block  of  carbide  is  formed  which  extends  practically  the 
whole  width  of  the  truck.  When  this  has  been  accom- 
plished, the  electrodes  are  entirely  withdrawn,  the  truck 
and  its  contents  removed,  and  another  empty  one  inserted 
in  its  place,  the  same  process  being  then  repeated. 

A  carbide  furnace, 
designed  and  patented 
by  Messrs.  J.  Zim- 
merman and  I.  S. 
Prenner,  poss  esses  a 
novel  distinction  in  the 
matter  of  feeding  ar- 
rangements for  the  raw 
material,  which,  instead 
of  being  introduced  into 
the  heat  zone  of  the  arc 
from  above,  as  usual,  is 
carried  up  by  a  screw 
conveyor,  from  below 
and  extruded  just  below 
the  active  extremities  of 
the  electrodes.  The  feed 
principle  may  be  likened  to  that  of  a  fountain. 

The  furnace  is  represented  in  Fig.  18  ;  the  mixture  of 
carbon  and  lime  is  fed  into  the  lateral  hopper  H,  and  passes 
thence,  down  the  inclined  conduit  C,  to  the  bottom  of  the 
screw  conveyor  A,  the  discharge  orifice  O  of  which  is  of 
smaller  diameter  than  the  conveyor  itself,  and,  as  shown, 
is  situated  at  the  top,  just  below  the  arcing  space  between 
the  electrodes  E  E.  In  passing  through  the  conveyor, 
which  is  driven  from  an  external  source  by  the  belt  or  chain 
B,  the  charge  undergoes  a  certain  amount  of  compression, 
exuding  finally  into  the  intensely  heated  area  of  the  arc, 
where  it  becomes  converted  into  carbide,  and  passes,  by 
gravitation,  down  the  annular  space  between  the  conveyor 

78 


FIG.  18. 


THEIR    INDUSTRIAL   APPLICATIONS 

casing,  and  the  inner  wall  of  the  furnace,  into  the  receiving 
truck  T,  which  can  be  removed  or  replaced  when  full,  thus 
rendering  the  process  continuous. 

A  patent,  granted  some  time  back  to  Dr.  Hugo  Koller, 
includes  an  arc  carbide  furnace  of  a  special  type,  adapted  for 
use  with  currents  of  higher  voltage  than  it  is  customary  to 
employ  for  the  purpose  of  carbide  production.  The  furnace 
itself  takes  the  form  of  a  long  narrow  conduit  of  refractory 
material,  the  length  of  which  is  governed,  to  a  certain  extent, 
by  the  voltage  to  be  employed  in  the  reaction.  Massive 
carbon  electrodes  are  introduced  through  the  end  walls, 
whilst  a  number  of  intermediate  carbon  blocks,  spaced  at 
regular  intervals  apart  along  the  length  of  the  furnace, 
and  depending  in  number  also  upon  the  voltage,  serve  to 
form  a  chain  of  inter-connecting  bi-polar  electrodes,  the 
space  between  each  pair  constituting  a  receptacle  for  the 
raw  material  and  carbide  formed  therefrom. 

The  intermediate  blocks  are  raised  on  suitable  supports 
out  of  contact  with  the  floor  or  hearth  of  the  furnace,  and 
the  latter  is  lined,  along  the  intervening  spaces,  with  shallow 
carbon  crucibles,  or  troughing,  which  assist  in  conducting 
the  current,  and  at  the  same  time  serve  as  receptacles  for 
the  carbide.  Only  a  small  portion  of  the  current  is  con- 
ducted along  these  carbon  troughs,  which  are  not  in  actual 
contact  with  the  electrode  blocks ;  the  main  reactions 
occur  through  the  heat  developed  in  the  several  arcs  formed 
between  each  neighbouring  pair  of  blocks. 

This  form  of  furnace  construction  is,  from  the  very  fact 
of  its  adaptability  to  circuits  of  comparatively  high  voltage, 
especially  applicable  to  large  units  for  the  commercial 
manufacture  of  calcium  carbide. 

A  carbide  arc  furnace,  patented  by  J.  H.  Morley,  has 
the  usual  interchangeable  hearths  and  automatic  feed 
arrangements,  the  distinctive  novelty  in  its  construction 
being  the  upper  carbon  electrode,  which  takes  the  form  of 
a  hollow  rectangular  conduit,  descending  vertically  into 

79 


ELECTRIC   FURNACES    AND 

the  furnace.  The  central  aperture,  or  bore,  of  the  carbon 
is  open  to  the  atmosphere,  and  furnishes  a  species  of  flue, 
or  chimney,  through  which  a  downward  current  of  air  is 
induced.  This  meets  the  active  charge,  at  the  very  point 
of  greatest  activity,  and  is  instrumental  in  preventing  over- 
heating and  explosions  of  gas  produced  in  the  reaction. 

The  process  is  rendered  more  thorough,  and  a  more  or 
less  continuous  furnace  action  secured,  by  a  reciprocating 
motion  communicated  to  the  central  carbon  electrode. 
In  addition  to  the  up  and  down  motion  thus  imparted,  a 
certain  turning  movement  is  also  given  to  the  conduit,  the 
motion  of  which  thus  resembles  the  turn  of  a  screw,  and 
tends  to  loosen  the  charge  of  carbon  and  lime  immediately 
surrounding  it,  and  bring  it  within  the  heat  zone  created 
by  the  arc. 

We  now  come  to  a  series  of  rotary  furnaces,  in  which  the 
hearth,  or  container,  for  the  raw  materials  under  treatment 
is  constructed  in  circular  form,  and  mounted  in  such  a 
manner  as  to  permit  of  its  being  revolved  like  a  wheel. 
Continuity  of  action  and  a  more  homogeneous  product  are 
claimed  for  this  class  of  furnace. 

The  Nikolai  principle  of  carbide  furnace  construction 
provides  for  a  continuous  process,  the  furnace  hearth  being 
revoluble,  and  the  raw  material  fed  in  at  one  point,  whilst 
the  carbide  is  withdrawn  at  another,  the  arc,  or  zone,  of 
activity  intervening. 

The  furnace  itself  consists  of  a  circular,  refractory  trough, 
which  constitutes  in  effect  the  tyre  of  a  wheel,  the  latter 
being  driven  at  a  suitable  speed,  by  gearing.  This  wheel 
and  the  attached  revoluble  hearth  constitute  one  electrode 
of  the  furnace,  the  other  being  fixed  at  a  given  point  above 
the  trough,  with  sufficient  clearance  for  the  charge  to  pass 
beneath  it,  through  the  heated  belt  formed  by  the  arc. 

The  mixture  of  coke  and  lime  is  fed  into  the  trough  at  a 
regular  rate  from  a  point  behind  the  fixed  electrode,  which 
latter  is  protected  by  a  heat-conserving  hood,  and,  having 

80 


THEIR    INDUSTRIAL    APPLICATIONS 

been  carried  under  it  by  the  revolution  of  the  wheel,  is 
converted  into  calcium  carbide  by  the  arc.  The  carbide 
thus  produced  then  passes  on,  and  is  removed  at  a  point 
in  advance  of  the  fixed  electrode  by  a  scraper,  leaving  the 
trough  free  for  the  reception  of  a  fresh  charge  when  it  again 
reaches  the  feeding  point. 

The  Horry  carbide  furnace  was  designed  by  Mr.  W.  S. 
Horry  with  a  view  to  overcoming  many  of  the  obvious 
defects  of  the  earlier  types  of  carbide  furnace.  Among 
the  principal  drawbacks  which  the  inventor  set  himself  to 
overcome  are  the  intermittent  nature  of  the  furnace  action, 
which,  in  many  cases,  necessitates  shutting  down  the  plant 
as  soon  as  the  furnace  is  full,  in  order  to  allow  the  contents 
to  cool  sufficiently  for  removal. 

Another  defect  arising  out  of  the  mode  of  adjustment 
and  general  disposition  of  the  electrodes  is  a  constantly 
changing  internal  resistance,  and  consequently  varying 
current,  under  which  circumstances  the  mass  of  carbide 
already  formed  is  again  in  part  subjected  to  the  further 
action  of  intense  heat,  tending  to  decompose  it,  whilst 
other  portions  of  the  charge,  out  of  the  immediate  zone  of 
heat,  remain  unconverted,  thus  leading  to  a  somewhat 
mixed,  and  by  no  means  homogeneous  product. 

The  constructional  principle  of  the  Horry  furnace  is  re- 
presented in  diagram  by  Fig.  19,  where  H  is  an  open 
fire-brick  hopper,  containing  the  mixture  of  lime  and  coke, 
and  supporting  at  its  lower  or  discharge  extremity  the 
two  carbon  electrodes  E  E,  which  are  bevelled  at  their 
active  edges,  in  order  to  present  a  vertical  surface  to 
the  arc.  The  length  of  the  latter  is  thus  maintained 
constant,  an  important  feature,  which  greatly  facilitates 
regulation. 

The  hopper  discharges  its  contents  between  the  flanges 
of  a  rotatable  metal  drum  D,  which  receives  the  carbide 
formed  in  the  arc,  and  retains  it  by  virtue  of  removable 
cover  plates  or  battens  B,  which  can  be  slid  into  place,  or 

81  G 


ELECTRIC    FURNACES    AND 


removed,  at  will,  As  the  formation  of  carbide  goes  on, 
the  drum  is  slowly  rotated  by  means  of  the  hand-wheel 
and  worm  W,  thus  conveying  the  carbide,  in  a  plastic  con- 
dition, away  from  the  region  of  the  arc. 

When  it  reaches  a  point  diametrically  opposite  to  the 
arc,  the  cover  plates  are  removed,  and  the  finished  product 
scraped  out,  leaving  that  portion  of  the  drum  free  for  the 

reception  of  a  fresh  charge  when 
it  again  comes  under  the  mouth 
of  the  hopper.  The  cooling  of 
the  product  is  thus  effected  grad- 
ually as  it  gets  farther  and 
farther  away  from  the  arc,  the 
heat  not  being  entirely  lost,  but 
in  part  communicated  to  the  un- 
converted portion  behind. 

The  action  need  never  be 
stopped  entirely,  and  the  speed 
of  rotation  of  the  wheel  is  regu- 
lated in  conformity  with  any 
variations  in  the  current  con- 
sumed by  the  furnace,  which  in- 
dicates sufficiently  how  the  con- 
version is  proceeding  at  the  par- 
ticular point  of  the  drum  which 
is  then  under  the  hopper.  The 
carbide  is  removed  in  a  plastic 
state. 

At  Sault  Ste.  Marie  a  Horry  carbide  plant  of  20,000  H.P. 
has  been  installed. 

The  Bradley  furnace,  patented  by  C.  S.  Bradley  in  1897j 
bears  a  striking  resemblance  to  the  Horry  carbide  furnace, 
in  that  it  consists  of  a  slowly  revolving  wheel,  which,  by 
bringing  fresh  materials  into  the  region  of  the  arc  and 
removing  the  resulting  carbide  therefrom,  renders  the  pro- 
cess continuous. 

82 


FIG.  19. 


THEIR    INDUSTRIAL   APPLICATIONS 

The  arrangement  consists  of  a  wheel,  with  semi-circular 
rim,  forming  one-half  of  a  circular  channel  for  the  reception 
of  the  raw  materials  and  the  carbide  formed  therefrom, 
the  other  half  being  constituted  by  semi-circular  sections, 
or  cover  plates,  which  are  latched,  or  otherwise  fastened 
on  the  descending  side  of  the  wheel  as  it  leaves  the  region 
of  the  arc,  and  removed  again,  on  the  ascending  side,  for  the 
withdrawal  of  the  product  and  unconverted  portion  of  the 
charge.  The  wheel  is  revolved  very  slowly  through  the 
medium  of  worm  gearing,  driven  by  an  electro-motor  ;  a 
structure,  15  ft.  in  diameter,  may,  according  to  the  specifi- 
cation, be  revolved  once  in  five  days. 

The  arc  is  either  created  between  a  single  carbon  electrode, 
4  in.  in  diameter,  adjustably  mounted  on  a  stand,  and 
arranged  to  strike  an  arc  with  a  temporary  carbon  core 
embedded  in  the  raw  material,  or  may  be  arranged  between 
two  oblique  electrodes,  operating  at  the  mouth  of  the  closed 
portion  of  the  rim.  In  the  former  case,  electrical  connexion 
with  the  temporary  core  is  secured  through  the  medium 
of  copper  bolts,  a  commutator,  and  fixed  brushes.  The 
arc,  once  struck,  is,  of  course,  maintained  between  the 
fixed  electrode  and  a  portion  of  the  core,  rendered  conduct- 
ing by  the  heat  of  the  reaction.  At  the  discharge  point, 
the  cover  plates,  as  before  stated,  are  removed,  and  the 
unconverted  portions  of  the  charge  fall  into  a  conveyor, 
which  returns  them  to  the  feed  side  of  the  wheel  to  again 
undergo  the  heating  process. 

By  treating  a  mixture  of  powdered  sand,  and  the  oxides 
of  calcium,  strontium  and  barium  respectively,  silicides  of 
these  metals  have  been  produced  in  the  Bradley  furnace, 
and  it  is  suggested  that  they  may  prove  of  ultimate  value 
in  the  various  dye  industries  from  the  fact  of  their  being 
powerful  reducing  agents. 

Mr.  C.  S.  Bradley  has  recently  modified  his  rotary  furnace 
construction,  the  modification  being  embodied  in  a  patent 
taken  out  during  1903,  which  provides  for  lining  the  sides 

83 


ELECTRIC   FURNACES   AND 

and  "  belly  "  of  the  drum  hearth  with  carbon  or  graphite 
plates,  thus  enabling  the  area  of  thermal  activity  to  be 
extended  throughout  the  entire  mass  of  material  under 
treatment,  without  fear  of  consequent  injury  to  the  struc- 
ture itself,  a  contingency  previously  avoided  by  a  layer  of 
unconverted  material. 

A  rotary  carbide  furnace  construction  has  also  been 
patented  by  Hudson  Maxim.  It  consists  of  a  drum  of 
somewhat  complicated  construction,  in  which,  according 
to  the  claims,  the  fused  carbide  is  held  against  the  inner 
surface,  whilst  any  excess  passes  out  through  the  open 
end  of  the  drum. 

A  somewhat  ingenious,  but  seemingly  commercially 
impracticable  form  of  construction  for  continuous  carbide 
furnaces  was  that  embodied  in  a  patent,  the  specification 
of  which,  by  Messrs.  J.  W.  Kenevel,  C.  A.  Spofford,  and  J.  H. 
Mead,  is  dated  August  24,  1897. 

In  general  principle  the  furnace  may  be  likened  to  a 
domestic  mangle,  or  rolling  mill,  and  consists  of  two  cylin- 
drical electrodes,  which  may  be  of  carbon,  between  which 
the  raw  mixture  of  coke  and  lime  is  fed  from  a  suitable 
hopper,  the  rate  of  feed  being  controlled  by  a  slide. 

Kerosene,  fed  on  to  the  moving  surfaces  of  the  rollers  by 
suitably  disposed  tubes,  acts  as  a  lubricant,  and  prevents 
the  carbide  from  adhering  thereto.  The  spindles  of  the 
rollers  are  insulated  from  them  by  glass  sleeves,  and  are 
carried  in  sliding  bearings,  pressed  together  by  springs, 
after  the  manner  of  a  mangle,  and  driven  by  gear  wheels 
carried  on  link  pieces. 

In  passing  between  the  electrode  rollers,  the  mixture  is 
converted  into  carbide  by  the  current,  which  is  conveyed 
to  them  through  the  medium  of  brushes  and  collector  rings, 
a  somewhat  difficult  problem  to  tackle  effectually,  when 
dealing  with  such  large  currents  as  are  called  for  in  electric 
furnace  methods.  The  carbide,  when  formed,  drops  below 
on  to  baffles,  placed  to  receive  it. 


THEIR    INDUSTRIAL    APPLICATIONS 

Messrs.  Lamoth  and  McRae,  of  Ottawa,  are  the  inventors 
of  a  resistance  furnace  for  the  production  of  calcium  car- 
bide, the  two  electrodes  being  bridged  by  carbon  pencils. 

M.  Raoul  Pictet  has  devoted  considerable  time  and 
attention  to  the  study  of  carbide  manufacture,  and  has 
designed  more  than  one  furnace  for  its  production.  His 
first  practical  experiment  was  conducted  with  a  species  of 
compound  furnace,  whereby  the  necessary  heat  was  obtained 
in  a  series  of  three  stages. 

At  the  top  was  an  ordinary  blast  furnace,  consuming 
coke  as  fuel,  and  into  which  the  cold  charge  of  coke  and 
lime  was  primarily  fed.  In  this  section,  it  attained  a  temper- 
ature of  1,980°C.  —  3,600°F.  It  then  passed  on  by  gravitation 
to  a  second  section,  where,  under  the  influence  o£  an  oxy- 
hydrogen  blow-pipe  flame,  its  temperature  was  still  further 
increased  to  2,368°C.  =  4,300°F.  Finally,  it  passed  into 
the  region  of  the  electric  arc,  where  a  temperature  of  from 
2,757°  to  3,312°C.  =  5,000°  to  6,000°F.  was  reached,  and 
the  combination  of  carbon  and  calcium  effected. 

In  a  subsequent  design,  the  blast  furnace  and  somewhat 
costly  blowpipe  sections  were  dispensed  with,  the  gradual 
preliminary  heating  of  the  charge  being  effected  instead 
by  the  waste  gases  from  the  furnace,  assisted  by  the  natural 
heat  arising  out  of  the  chemical  combination. 

Two  carbide  furnaces  of  this  description,  constructed 
under  M.  Pictet's  patents,  were  built  some  few  years  back 
at  Ingleton,  for  the  then  Ingleton  Carbide  Company. 
Each  furnace  required  2,000  amperes  to  work  it,  and  con- 
sisted of  a  hearth  some  2  ft.  square,  by  3  ft.  high,  built  of 
bauxite  bricks,  cased  on  the  outside  with  a  layer  of  fire- 
brick, and  mounted  on  foundations  of  ordinary  brick, 
sufficient  space  being  left  below  for  the  introduction  and 
withdrawal  of  a  truck  for  the  reception  of  the  carbide 
formed  therein. 

The  carbon  electrodes  were  square  in  section,  with  6-in. 
sides,  the  negative  being  mounted  at  an  angle  of  30° 

85 


ELECTRIC    FURNACES    AND 

with  the  horizontal,  whilst  the  positive  was  horizontal,  and 
adjustable  for  feed  purposes,  the  latter  being  effected  by  a 
hand  wheel  and  screw  motion. 

Each  electrode  entered  the  furnace  proper  through  a 
sheet  iron,  water- jacketed  gland,  whilst  the  terminal  con- 
nexion itself,  described  separately  in  another  portion  of 
the  book,  was  also  water- jacketed. 

Water  circulation  was  secured  by  means  of  high  level 
tanks,  one  to  each  electrode  circuit.  The  electrical  insula- 
tion of  the  circulatory  system  was  further  secured  by  mount- 
ing the  water  tanks  on  wooden  bases,  and  by  the  introduc- 
tion of  6-in.  lengths  of  rubber  tubing,  in  all  pipe  connexions, 
both  supply  and  waste. 

An  opening  was  provided  in  the  bottom  of  the  furnace 
proper  for  the  discharge  of  carbide  into  the  truck  placed 
to  receive  it,  whilst  a  flue,  also  in  connexion  with  the  dis- 
charge orifice,  conducted  such  heated  gaseous  products  as 
escaped  with  the  carbide  through  a  space  between  the 
furnace  linings  to  the  top,  whence  an  iron  tube,  enclosed 
in  a  fire-brick  flue,  and  inclined  at  an  angle  of  25°,  led  up 
from  the  furnace  to  a  suitable  point  above,  where  the  iron 
tube  penetrated  the  fire-brick  wall  of  the  flue,  the  latter 
being  bent  at  right  angles,  for  the  purpose,  and  continued 
upwards  to  form  a  feed  hopper  or  chute,  down  which  the 
mixture  of  coke  and  lime  was  fed  in  the  form  of  compressed 
briquettes. 

The  hot  gases  of  combustion  passed  up  between  the 
inner  flue  wall  and  the  iron  tube  to  the  outer  end,  which 
effected  a  junction  with  the  chimney  shaft.  In  their  pas- 
sage they  served  to  impart  a  preliminary  degree  of  heat  to 
the  descending  charge  in  the  iron  tube. 

The  furnace  action  was  started,  and  a  primary  draught 
created  by  an  ordinary  fire,  which  was  lit  within  a  space 
provided  for  the  purpose  between  the  two  furnaces. 

The  original  Pictet  furnaces  at  Ingleton  have  since  been 
replaced  by  Parker  furnaces,  described  on  page  94. 

86 


THEIR    INDUSTRIAL   APPLICATIONS 

Pictet  estimates  that  by  the  economies  consequent  on 
efficient  preheating , of  the  raw  materials  in  calcium  carbide 
manufacture,  the  cost  can  be  reduced  to  £3  85.  per  ton. 

Dr.  Borchers'  improved  method  of  carbide  production 
involves  several  distinctly  novel  points,  chief  among  which 
may  be  mentioned  the  utilization  of  the  excess  heat  evolved 
for  producing  steam  in  an  encircling  boiler,  or  large  water 
jacket,  which  surrounds  the  furnace  ;  any  excess  of  heat 
over  and  above  that  required  in  the  process  of  carbide 
formation  is  thus  utilized  in  the  generation  of  steam,  which 
may  serve  in  turn  for  driving  an  engine,  thus  effecting  a 
considerable  saving. 

This  suggestion,  of  totally  enclosing  the  furnace  and  its 
contents  in  a  water  jacket,  possesses  also  the  attendant 
advantage  that  any  unconverted  charge  remaining  at  the 
end  of  the  operation  can  be  withdrawn  cool,  and  its  ad- 
mixture of  carbon  thereby  preserved  from  the  combustion 
which  usually  ensues  when  the  unconverted  remainder  of 
an  ordinary  carbide  furnace  charge  is  exposed  to  the  air. 

The  drawbacks  incidental  to  existing  types  of  carbide 
furnace,  which  Dr.  Borchers'  improved  construction  is 
intended  to  overcome,  are — 

(1)  Partial  combustion  of  unconverted  carbon  when  the 
charge   is   withdrawn,    and   consequent   contamination   of 
the  remainder  by  ash,  together  with  the  necessary  addition 
of  fresh  carbon. 

(2)  Particles  of  dust  are  carried  over  by  the  resultant 
gases  and  inconvenience    the    attendants,  besides    adding, 
by  their  combustible  nature,  to  the  danger  of  fire. 

(3)  The  amount  of  power  consumed  in  carbide  manu- 
facture is  abnormal. 

In  addition  to  the  above  novel  feature  of  water-jacket- 
ing the  entire  furnace,  which  is  accordingly  constructed 
with  very  thin  walls,  Dr.  Borchers  proposes  to  work  his 
carbide  furnaces  on  the  following  plan — 

In  the  resistance  type,  a  heating  core  of  carbon  is  packed 

87 


ELECTRIC   FURNACES   AND 

between  two  carbon  electrodes,  situated  at  opposite  ends 
of  the  furnace,  and  surrounded  by  a  filling  of  lime.  Cur- 
rent is  then  switched  on  and  heats  the  carbon  column, 
with  the  result  that  the  layer  of  lime  in  immediate  contact 
with  it  is  fused,  and  enters  into  combination  with  the  carbon 
to  form  carbide,  which  flows  away  to  the  bottom  of  the 
furnace.  A  fresh  layer  of  lime  takes  its  place,  and  the 
reaction  is  repeated,  or  rather  continued,  until  the  whole 
of  the  carbon  forming  the  resistance  is  used  up,  when  the 
current  is  switched  off,  and  the  resulting  carbide,  after 
having  been  allowed  to  cool,  removed. 

In  Dr.  Borchers'  arc  furnace  the  electrodes  are  disposed 
vertically,  the  upper  descending  axially  through  a  hopper, 
which  also  serves  to  feed  the  charge  into  the  furnace,  and 
the  lower  one  passing  up  to  meet  it,  through  a  hinged  trap- 
door in  the  hearth  or  base  of  the  furnace,  which  can  be 
opened  at  the  end  of  the  operation,  for  withdrawal  of  the 
carbide  formed. 

To  commence  with,  a  mixed  charge  of  coke  and  lime  is 
well  rammed  into  the  furnace  around  the  electrodes  and 
the  hopper,  whilst  the  latter  is  also  filled  with  a  coarsely 
ground  charge  of  raw  material,  to  such  a  depth  as  to  pre- 
vent the  escape  of  the  gases  evolved  in  the  reaction.  In 
the  upper  portion  of  the  furnace,  remote  from  the  actual 
heat  zone,  is  located  an  inclined  metal  plate,  perforated  to 
allow  the  passage  of  the  furnace  gases,  and  packed,  above, 
with  a  layer  of  wood  shavings,  or  other  suitable  material, 
to  act  as  a  filter  on  the  gases  passing  through,  and  free 
them  from  the  dust  and  solid  particles  which  they  would 
otherwise  carry  with  them  out  of  the  furnace. 

The  dimensions  of  the  furnace  are  such  that  when  the 
operation  is  completed,  a  block  of  carbide  is  formed  in  the 
centre,  surrounded  on  all  sides  by  a  layer  of  unconverted 
charge,  which  remains  non-conducting  by  virtue  of  the  water- 
cooled  walls.  This  block  is  left  to  cool  for  a  few  hours  before 
withdrawal,  the  excess  heat  stored  up  in  it  being,  as  before 

88 


THEIR    INDUSTRIAL    APPLICATIONS 

mentioned,  absorbed  by  the  surrounding  water  and  thereby 
utilized  in  the  generation  of  steam  for  power  purposes. 

A  patent  taken  out  by  Ricardo  Memmo  in  1897  relates 
more  especially  to  two  improvements,  continuity  of  furnace 
action,  and  pre-heating  of  the  charge,  in  the  efficiency  of  the 
process  of  carbide  manufacture,  and  covers  a  form  of  construc- 
tion in  which  the  furnace  proper  is  tubular,  with  a  movable 
graphite  hearth.  This  latter  is  supported  on  an  iron 
foundation,  which  can  be  raised  or  lowered  as  required  by 
either  a  screw,  or  rack  and  pinion  motion.  To  commence 
with,  the  hearth  is  adjusted  at  a  point,  just  below  the  upper 
electrode,  the  raw  mixture  to  be  converted  being  fed  in 
by  a  screw  conveyor,  from  a  hopper,  provided  with  a 
refractory  lining. 

In  order  to  effect  the  pre-heating  of  the  charge,  water  is 
included  in  the  mixture  supplied  to  the  hopper,  and  forms 
water  gas,  which  is  burnt,  to  heat  the  air  supplied  to  a 
circulatory  system,  which  includes  both  the  jacketed  walls 
of  the  furnace,  and  the  hopper  itself. 

La  Societa  Italiana  del  Forni  Electricci,  Italy,  about 
this  time,  took  out  a  patent  for  a  carbide  furnace,  in  which 
the  gases  of  combustion  were  similarly  employed,  after 
purification  and  storage,  to  pre-heat  the  raw  material, 
which  was  delivered  through  an  elliptical  tube  by  a  screw 
feed  motion.  The  electrodes  consisted  of  carbon  blocks, 
one  of  which  was  adjustable  by  means  of  a  lever  to  which 
it  was  attached  by  a  metal  clamp,  or  plate.  The  furnace 
was  lined  with  carbon,  and  the  combustion  gases  passed  out 
through  orifices  in  the  walls  of  the  chamber  to  a  suitable 
collecting  point,  where  they  were  duly  collected,  purified, 
and  stored,  as  described  above,  to  be  ultimately  consumed 
in  pre-heating  the  charge  before  its  entry  into  the  furnace 
proper. 

The  three-phase  carbide  furnaces  designed  and  patented 
by  Ricardo  Memmo  have  been  in  use  at  St.  Marcello  d'Aosta, 
Italy,  since  1897.  Charcoal  is  employed  in  place  of  the 


ELECTRIC    FURNACES    AND 


more  usual  coke  to  provide  the  carbon  necessary  to  the 
combination.  Wood,  from  the  abundant  supply  pro- 
vided by  the  vast  forests  of  the  Alps,  is  converted  into 
charcoal  in  gas  retorts,  the  resultant  gas  being  again  utilized 
in  heating  other  furnaces  for  baking  both  the  lime  and 
mixture  of  the  latter  with  charcoal.  Charcoal  and  lime, 
having  been  individually  subjected  to  the  baking  process, 
are  next  pulverized,  and  subsequently  mixed  in  the  correct 
proportion  for  the  production  of  calcium  carbide.  Small 
quantities  -of  water  and  tar  are  added,  to  secure  agglomera- 
tion, and  the  mass  is 
formed,  by  a  machine, 
into  bricks,  which  are 
subsequently  baked  in 
a  furnace  heated  by  the 
gaseous  products  of  the 
electric  furnaces.  These 
bricks  constitute  the 


FIG.  20. 


raw  material  with  which 
the  furnaces  are  fed, 
and  it  is  worthy  of 
note  that,  treated  in 
this  manner,  little  or  no 
dust,  which  gives  rise  to 
considerable  trouble  in 
carbide  furnaces  fed  in 
the  ordinary  manner  with  a  pulverized  charge,  is  formed. 

The  types  of  carbide  furnace  in  use  at  St.  Marcello,  are  both 
intermittent  and  continuous  in  action.  The  former,  Fig.  20, 
is  extremely  simple  in  construction,  and  consists  of  a  cubical 
chamber  A,  built  of  refractory  brick,  cased  externally  with 
ordinary  brick  B.  The  floor  or  hearth  H  is  compressed 
magnesium  oxide,  or  lime,  and  an  iron  door,  lined  internally 
with  refractory  brick,  serves  for  the  removal  of  the  carbide 
formed. 

Above  the  door  is  a  feed  orifice,   through  which  pro- 

90 


THEIR    INDUSTRIAL    APPLICATIONS 

jects  a  cast-iron  chute,  down  which  the  bricks  are  fed  into  the 
furnace,  whilst  in  the  opposite  wall  is  a  flue  F  for  convey- 
ing away  the  gases  formed  in  the  conversion,  to  be  ulti- 
mately used  in  baking  the  bricks,  as  already  described.  The 
three  carbon  electrodes  C  C  C  enter  through  the  arched 
roof  R,  which  is  also  of  refractory  brick  ;  they  are  each 
five  inches  in  diameter,  and  are  supported  by  holders,  on 
the  extremities  of  large  iron  rods,  threaded  for  the  greater 
portion  of  their  length,  and  passing  through  bronze  nuts  N, 
supported  on  cast-iron  plates  P,  which  cover  the  openings  in 
the  furnace,  any  remaining  space  being  cemented  up  with  a 
mixture  of  graphite  and  glue.  Hand  wheels  W  are  attached 
to  these  nuts,  and  serve  to  adjust  the  relative  positions  of 
the  three  carbons  inside  the  furnace. 

The  capacity  of  the  latter  is  seventy  cubic  feet. 

To  commence  with,  the  carbons  are  lowered  until  they 
make  contact  with  a  short-circuiting  plate  of  graphite,  and 
the  interior  of  the  furnace  is  filled  with  bricks,  duly  prepared 
as  described  above  ;  a  lining,  about  half  an  inch  thick,  of 
unconverted  mixture  is  usually  left  adhering  to  the  walls 
from  the  previous  operation  ;  it  protects  the  structure  from 
excessive  heat,  and,  incidentally,  prevents  the  newly 
formed  carbide  from  adhering  to  the  walls.  The  furnace 
door  is  closed,  and  all  spaces  luted  with  clay  or  lime. 

The  generating  plant  is  then  started  up,  and  the  load 
soon  attains  its  normal  value,  viz.,  1,200  amperes  on  each 
circuit,  at  145  volts.  After  about  half  an  hour,  the  furnace 
is  fed  through  the  main  door,  and  subsequent  regulation 
is  effected  according  to  the  readings  on  the  ammeters, 
which  are  included,  one  in  each  circuit. 

The  furnaces  are  charged  once  every  quarter  of  an  hour,  to 
make  up  for  the  decrease  in  volume  of  the  charge  arising 
out  of  the  conversion.  A  complete  operation  lasts  about 
five  hours,  after  which  the  current  is  switched  on  to  the 
next  furnace.  Another  interval  of  five  hours  is  then  necessary 
in  order  to  permit  the  contents  of  the  furnace  to  solidify, 


ELECTRIC    FURNACES    AND 


when  they  are  removed,  red  hot,  by  means  of  iron  bars, 

Each  block  of   carbide    thus   formed  weighs    from  150  to 

250  kilogrammes,  and  is  left  for  some  considerable  time  to 

cool  before  it  is  broken  up. 

The   output    of    carbide   manufactured  at   St.    Marcello 

works  out  at  4' 37  kgs.  per  k.w.  day  of  twenty-four  hours, 

but,  according  to  UElectri- 
cien,  July  8,  1899,  this  fig- 
ure has  been  increased  to 
4*88  kgs.  per  k.w.  day. 

The  consumption  of  elec- 
trodes during  one  opera- 
tion of  the  furnace  is  4*5 
to  5  kgs.,  or  24s.  per  ton  of 
carbide  produced.  The 
figure  is  a  high  one,  and  is 
attributed  mainly  to  the 
frequent  stoppages  for  dis- 
charging and  recharging, 
during  which  a  wasteful 
combustion  of  the  electrode 
carbon  goes  on. 

In  the  continuous  carbide 
furnace  operated  at  St. 
Marcello,  the  three  elec- 
trodes E  E  (Fig.  21)  are 
grouped  "  star  "  fashion, 
and  the  arcs  are  struck  be- 
tween them  and  a  common 

carbon     electrode  C,  which  constitutes  the   hearth  of   the 

furnace. 

The  latter  is  a  cylindrical  structure  R  of  refractory  brick, 

the  three  carbon  electrodes  entering  at  an  angle  through  the 

upper  walls,  and  being  supported  and  fed  downwards  in  a 

similar  manner  to  the  foregoing. 

The  feed  hopper  H  is  situated  over   the  centre  of  the 

92 


FIG.  21. 


THEIR    INDUSTRIAL   APPLICATIONS 

furnace,  above  the  carbons,  whilst  the  hearth,  which  con- 
sists of  a  cast-iron  plate  F  covered  with  several  layers  of 
graphite  C,  is  supported  on  a  central  screwed  stem  S,  and 
can  be  raised  or  lowered  throughout  the  entire  height  of  the 
furnace  by  means  of  a  hand  wheel  and  gearing  W.  To 
commence  with,  it  is  raised  until  the  graphite  plate  makes 
contact  with  the  three  carbon  electrodes,  and  is  gradually 
lowered  by  means  of  its  hand  wheel,  as  the  operation  pro- 
ceeds, and  fresh  material  is  fed  in. 

As  the  process  of  carbide  formation  goes  on,  the  hearth, 
as  already  stated,  is  gradually  lowered,  making  room  for  more 
carbide,  and  a  further  supply  of  raw  material.  At  a  certain 
point,  the  remaining,  partially  converted  and  unconverted 
charge  is  gripped  and  held  by  three  clamping  jaws,  operated 
by  screws,  whilst  the  carbide  already  formed  is  removed  at 
the  base  of  the  furnace,  and  the  hearth  re-adjusted  for  the 
reception  of  a  fresh  charge. 

Six  or  seven  hours'  continuous  working  suffice  to  bring 
the  hearth  to  its  lowest  point,  with  a  column  of  finished 
carbide  above  it,  surmounted  by  a  layer  around  the  arcs,  in 
which  the  process  of  conversion  is  still  going  on.  A  door  at 
the  base  of  the  structure  permits  of  the  removal  of  the  car- 
bide first  formed,  and  the  process  is  thereby  rendered 
continuous. 

Regulation  is  effected  by  moving  the  hearth  only,  the 
adjustment  of  the  carbons  themselves  being  only  of  a  nature 
to  compensate  for  their  consumption. 

The  Parker  carbide  furnace,  designed  and  patented  by 
Mr.  A.  Parker,  of  Chorley,  has,  for  its  main  object,  the 
securing  of  a  more  wide-spread  action  throughout  the  mass 
of  unconverted  material,  with  a  consequent  lessening  of  the 
crust  or  unconverted  residue,  which  is  always  present  in  car- 
bide furnaces,  and  has  to  be  either  mingled  with  the  carbide 
formed,  thereby  decreasing  its  efficiency  as  a  gas  producer, 
or  again  subjected  to  the  action  of  the  furnace  in  conjunc- 
tion with  the  next  charge  to  be  introduced. 

93 


ELECTRIC   FURNACES    AND 

The  Parker  furnace,  the  principle  of  which  is  represented 
in  sectional  plan  by  Fig.   22,  consists  of  a  slowly  rotating 
cylindrical   crucible  A,    lined  with   carbon  C,  which   con- 
stitutes the  negative  electrode,  and  a  rectangular  vertical 
block,  B,  which  forms  the  positive  electrode,  and  is  placed 
axially  within  the  crucible,  A.      The  slow  rotation  of  the 
latter,  coupled  with   a  simultaneous  upward  motion,  com- 
municated  to    the    electrode    B, 
serves    to  build   up   a   solid  and 
homogeneous    block    of    carbide, 
surrounded  by  a  very  thin  crust 
of    unconverted    material.       The 
corners  of   the  electrode  B,  com- 
ing, as  they  do,  into  close  prox- 
imity with  the   inner  wall  of   A, 
effectually    agitate    the    contents 
FIG.  22.  during  the  process   of  conversion, 

whilst  the  arc  is  constantly  moved 

from  one  point  to  another,  thereby  tending  to  homogeneity 
of  action.  The  feed  hopper  inlets  i  i  are  arranged,  one  on 
either  side  of  the  positive  electrode  B  at  the  upper  portion 
of  the  furnace,  and  a  regular  feed  is  automatically  secured. 
The  process  of  removing  a  full  crucible,  substituting  an 
empty  one,  and  readjusting  the  electrode  B  preparatory  to 
again  switching  on  the  current,  is  said  to  occupy  only  three 
minutes. 

In  a  modified  form  of  this  furnace,  a  flattened  or  ovoid 
electrode  is  substituted  for  the  rectangular  formation  shown 
in  the  figure. 

The  Parker  carbide  furnace  is  now  in  use  by  the  Acetylene 
Gas  and  Electric  Smelting  Company,  Ltd.,  who  have  pur- 
chased the  patent  rights,  having  superseded  the  original 
Pictet  furnaces  which  were  installed  by  the  Ingleton  Water 
Power  Company. 

The  type  of  furnace  employed  by  the  United  Alkali  Com- 
pany, at  Widnes,  resembles  that  devised  by  Parker.  It 

94 


THEIR    INDUSTRIAL   APPLICATIONS 


operates  on  the  resistance  principle,  the  upper  electrode  being 
continuously  embedded  in  the  charge,  whilst  the  remaining 
electrode  is  integral  with  the  crucible  containing  it. 

In  operation,  the  latter  is  slowly  rotated,  and  the  upper 
electrode  gradually  raised,  raw  material  being  fed  in  mean- 
while, until  a  block  of  carbide,  practically  equal  to  the  capa- 
city of  the  crucible,  has  been  built  up.  By  this  continuous 
relative  movement  of 
the  charge  and  elec- 
trodes, equivalent,  in 
point  of  fact,  to  a  slow 
stirring  motion,  very 
complete  action  is  se- 
cured, and  but  little  of 
the  contents  of  the 
crucible  remain  uncon- 
verted. 

In  1901,  Dr.  Oscar 
Frohlich,  of  Steglitz, 
Germany,  patented  and 
assigned  to  the  Siemens 
and  Halske  Company, 


of   Berlin,  a   somewhat 
ingenious   carbide    fur- 
nace, the  principal  nov-  FIG.  23. 
elty    in  which   consists 

in  the  collection  and  utilization  of  the  otherwise  waste  gases, 
mainly  carbon  monoxide,  resulting  from  the  reaction  itself. 
The  furnace  in  which  Dr.  Frohlich  effects  this,  is  repre- 
sented in  Fig.  23,  and  consists  of  a  cylindrical  iron 
crucible  A,  lined  interiorly  with  fire-clay  F,  and  a  sloping 
funnel-shaped  carbon  hearth  C,  which  forms  one  electrode 
of  the  device,  and  centres  in  a  discharge  orifice  or  outlet  0 
for  the  carbide.  The  other  electrode  T,  also  of  carbon, 
takes  the  form  of  a  vertical  tube,  or  flue,  the  upper  end  of 
which  is  capped  and  fitted  with  the  tubular  conduits  c  c, 

95 


ELECTRIC   FURNACES   AND 

which  curve  over  as  shown,  and  descend  to  an  annular  flue 
/,  disposed  around  the  lower  portion  of  the  crucible. 

The  carbon  monoxide  and  other  reaction  gases  pass  up 
through  the  central  tubular  carbon  electrode  T,  and  by 
way  of  the  conduits  c  c  to  the  flue  /,  where  they  are  burnt 
in  admixture  with  air,  which  enters  through  holes  in  the 
flue  walls.  The  products  of  combustion  pass  off  by  way  of 
the  pipe  P.  The  heat  of  combustion  of  the  reaction  gases, 
which,  collected  in  this  manner,  are. almost  entirely  free  from 
dust,  is  thus  utilized  in  auxiliary  heating  of  the  crucible 
contents. 

The  carbide  formed  falls  through  the  orifice  O  on  to  the 
outer  surface  of  the  conical  table  D,  which  is  lipped  to 
retain  it.  This  receiving  cone  is  carried  by  a  vertical  stem, 
which  can  be  raised  or  lowered  in  its  standard  S  by  means 
of  the  lever  H ;  its  position,  relatively  to  the  crucible,  can 
thus  be  adapted  to  either  intermittent  or  continuous  action 
of  the  furnace,  as  may  be  desired. 

Mr.  Alfred  H.  Cowles  has  recently  patented  some  details 
in  the  process  of  calcium  carbide  manufacture,  which,  among 
other  things,  include  the  utilization  of  the  carbon  monoxide 
gas  given  off  for  the  purpose  of  pre-heating  the  charge.  In 
Dr.  Frohlich's  invention,  already  described,  the  gas  is 
used  rather  as  an  auxiliary  to  the  electric  heating  in  the 
furnace  itself. 

A  form  of  carbide  furnace  construction,  based  upon 
Cowles'  latest  patent,  is  depicted  in  Pig.  24.  It  consists 
of  an  inverted  cone-shaped  crucible  A,  of  iron,  lined 
interiorly  with  refractory  non-conducting  material  R. 
The  hearth  of  the  furnace  consists  of  a  solid  carbon  block 
B,  also  protected  by  an  iron  casing,  and  electrically  separated 
from  the  main  body  of  the  furnace  by  a  layer  of  insulating 
material  L.  This  carbon  block  also  constitutes  one  fixed 
electrode,  the  others  E  E  consisting  of  carbon  rods,  dis- 
posed radially,  like  the  spokes  of  a  wheel,  through  the  upper 
part  of  the  furnace  walls. 

96 


THEIR    INDUSTRIAL   APPLICATIONS 


A  cursory  study  of  this  form  of  construction  will  show 
that  the  heating,  being  effected  on  the  resistance  principle, 
is  most  concentrated  at, 
or  near,  the  hearth  itself, 
where  the  various  current 
paths  converge.  The  ob- 
ject of  this  concentration 
is  to  secure  a  molten  pro- 
duct which  can  be  run  off 
at  the  tap  hole  T  pro- 
vided in  the  hearth. 

Mounted  axially  in  the 
centre  of  the  lid  D,  which 
effects  a  gas-tight  junction 
with  the  furnace  proper, 
is  a  pre -heating  chamber 
or  tower  H,  having  a  feed 
aperture  at  the  top.  It 

consists,  like   the  furnace,  FlG   24. 

of  an  iron  shell,  lined  with 

refractory  material,  and  through  its  walls,  a  short  distance  up 
from  the  furnace  lid,  pass  pipes,  P  P,  which  communicate 
with  the  main  furnace  chamber  as  shown,  and  serve  to  convey 
the  carbon  monoxide  and  other  gases  to  burners  in  the 
pre-heating  tower,  where  they  are  burnt  in  conjunction  with 
a  blast  of  air  introduced  through  the  smaller  pipes  p  p 
after  the  manner  of  a  blow-pipe. 

The  descending  charge  thus  receives  a  preliminary  heating 
before  entering  the  furnace,  an  initial  elevation  of  its 
general  temperature,  which  should  effect  considerable 
economy  in  the  current  necessary  to  complete  the  process 
of  carbide  formation. 

A  form  of  arc  furnace,  invented  by  R.  C.  Contardo,  which 
is  applicable,  with  some  slight  modifications,  to  either 
calcium  carbide  manufacture,  or  the  smelting  of  metallic 
ores,  consists  of  a  refractory  chamber,  with  curved,  or 

97  H 


ELECTRIC   FURNACES   AND 


contracted  hearth,  immediately  above  which  are  disposed  the 
two  electrodes.  Above  these  again,  and  meeting  at  an 
angle  over  the  arc,  are  two  inclined  plates  which  may  be 
of  graphite,  or  other  equally  suitable  material.  These  form, 
together  with  the  downwardly  sloping  walls  of  the  furnace 
itself,  a  couple  of  inclined  passages  or  chutes,  down  which 
the  raw  material  is  fed  from  a  central  orifice  above. 

By  virtue  of  their  position,  immediately  above  the  arc, 
the  sloping  plates  become  intensely  hot,  and  communicate 
their  heat  to  the  descending  charge,  which  is  thus  pre-heated 
before  entering  the  active  centre  of  the  furnace,  immediately 

below    the     electrodes,    where 
the  operation  is  concluded. 

In  general  construction,  the 
above  furnace  is  very  similar  to 
that  illustrated  in  Fig.  32. 

The  King  carbide  furnace 
turns  out  its  product  in  "block  " 
form.  The  hearth  consists  of 
a  truck  T  (Fig.  25),  at  the 
bottom  of  which  is  a  slab  of  car- 
bon C,  forming  one  electrode 
of  the  furnace,  the  other,  E,  be- 
ing vertically  adjustable.  The 
truck  is  mounted  on  rails,  and 
provided  with  a  mechanical 
attachment,  not  shown  in  the 
figure,  whereby  a  small  recip- 
rocating movement  is  communicated  to  it,  during  the 
action  of  the  furnace,  tending  to  shake  down  and  level  the 
charge.  It  is  enclosed  in  a  brickwork  chamber  B,  down 
inclined  channels  a  a,  in  the  walls  of  which  the  raw 
material  is  fed.  As  the  operation  proceeds,  the  upper 
electrode  E  is  gradually  raised,  whilst  fresh  material  is 
fed  in,  until  the  truck  is  full  of  carbide  together  with  partially 
converted  raw  material.  It  is  then  allowed  to  cool,  run  out 

98 


FIG.  25. 


THEIR    INDUSTRIAL    APPLICATIONS 

of  the  chamber  B,  and  emptied,  the  carbide  being  separated 
from  the  unconverted  material,  and  the  latter  worked  up 
into  the  next  charge. 

Air  ducts,  not  shown  in  the  figure,  are  provided  within  the 
walls  of  the  structure,  which,  by  circulation  of  the  air 
within  them,  serve  to  keep  the  inactive  portions  of  the 
furnace  fairly  cool,  and  confine  the  centre  of  thermal 
activity  to  the  truck  hearth. 

The  furnace  employed  at  the  works  of  the  Deutsche 
Gold  und  Silberscheide  Anstalt  consists  of  a  removable 
hearth,  or  coke-lined  truck,  which  also  constitutes  one 
electrode,  and  a  fixed  upper  structure  of  refractory  brick- 
work, which  surrounds  the  truck  when  in  its  working 
position,  and  assists  in  conserving  the  furnace  heat. 

The  upper  carbon  electrode  is  adjustable,  and  passes 
through  an  aperture  in  the  roof,  as  do  also  the  feed  inlet, 
and  a  pipe  for  conveying  away  the  carbon  monoxide  gas 
formed  in  the  reaction. 

To  commence  with,  the  truck  hearth,  previously  filled 
with  a  granular  mixture  of  coke  and  lime,  is  run,  on  rails, 
to  a  point  immediately  beneath  the  hood,  into  which  it  is 
then  raised,  vertically,  by  chains  and  pulleys,  until  its  lower 
projecting  flange  effects  a  gas-tight  junction  with  the 
lower  rim  of  the  fixed  structure  above. 

The  upper  adjustable  electrode  is  then  lowered  into 
position  through  the  opening  provided  for  it  in  the  hood, 
and  the  current  switched  on.  A  current  of  from  2,000  to 
3,000  amperes  at  60  to  65  volts  is  required  to  operate  the 
furnace,  and  an  output  of  five  kilogrammes  of  carbide  per 
kilowatt  day  is  said  to  be  secured,  the  resultant  product 
being  85  per  cent,  pure  carbide.  The  upper  carbon  electrode 
is  consumed  at  the  rate  of  about  50  kgs.  per  ton  of  carbide 
produced. 

In  carbide  furnaces  designed  for  continuous  action,  some 
difficulty  is  experienced  in  securing  the  requisite  regularity 
of  action,  owing  to  the  time  expended  in  raising  each  batch 

99 


ELECTRIC    FURNACES    AND 


of   raw  material  which  arrives  at    the  heat  zone  to  the 
temperature  necessary  for  effecting  combination. 

The  action  is  thus  jerky  and  intermittent,  rather  than 
continuous. 

A  German  patent,  the  principle  of  which  is  illustrated 
in  Fig.  26,  has  in  view  the  elimination  of  this  defect.  It 
relates  to  a  continuous  carbide  furnace,  in  which  one 
electrode,  A,  is  vertical,  whilst  the  other,  B,  is  inclined  to 
it,  meeting  it  at  the  lower  extremity,  with  the  exception 
of  the  necessary  arcing  space.  The  furnace  hearth  F 

is  also  inclined  at  an  angle,  which 
coincides  with  that  of  the  elec- 
trode B,  and  its  walls,  moreover, 
converge,  to  form  a  species  of 
funnel,  or  tapering  conduit,  with 
its  smallest  extremity  situate  at 
the  meeting  point  of  the  elec- 
trodes, where  also  the  discharge 
orifice  for  the  finished  carbide  is 
located. 

The  raw  charge,  fed  in  at  the 
_^  widest  dimension  of  the  furnace, 
thus  forms  a  bridge  between  the 
electrodes  for  the  greater  part  of 
their  length,  the  resistance  of 
which  varies  inversely  with  the 
cross-section.  The  heating  effect 

is  thus  gradually  increased,  as  the  mixture  of  coke  and  lime 
travels  towards  the  arcing  zone,  and  is  finally  concen- 
trated in  the  region  of  the  arc,  where  the  operation  is  com- 
pleted and  the  carbide  withdrawn. 

Energy  Required  in  Calcium  Carbide  Manufacture. — 
Blount's  theoretical  estimate  of  the  energy  necessary  to 
produce  calcium  carbide  is  thus  arrived  at — 

"  Moissan  has  shown  that  the  heat  of  formation  of  calcium 
oxide  is  145  Calories,  and  that  the  reaction, 

100 


FIG.  26. 


THEIR    INDUSTRIAL  APPLICATIONS 
CaO+  3C=CaC2  +  CO, 

takes  place  at  3,300°C=  5,972°F.  The  specific  heat 
of  CaO  may  be  taken  as  approximately  0-12  ;  that  of 
carbon  as  0-47.  The  energy  necessary  to  raise  56  grammes 
of  CaO  and  36  grammes  of  C  to  this  temperature 
is  79*5  Calories.  The  formation  of  calcium  carbide  from 
Ca  and  C  is  esteemed  an  endothermic  reaction,  requiring 
48  Calories.  The  total  energy  needed  is,  therefore, 

79-5  +  145  +  48   Calories  =  272-5   Calories. 

From  this  must  be  deducted  the  energy  evolved  by 
the  oxidation  of  carbon  to  CO,  i.e.,  29  Calories.  There- 
fore, the  energy  to  be  supplied  to  form  64  grammes  of 
CaC2  is  243-5  Calories. 

"  In  this  calculation,  the  energy  evolved  or  absorbed  by 
the  formation  of  CaC2  from  Ca  and  C2  is  a  doubtful  quantity. 
No  reliable  data  have  been  arrived  at.  The  estimate  given 
is  likely  to  err  on  the  right  side,  the  more  so  as  no  credit 
has  been  taken  for  possible  regeneration  by  utilizing  the 
sensible  heat  of  one  charge  for  warming  up  the  next. 

"  Thus  it  may  be  taken,  for  practical  purposes,  that  the 
formation  of  one  ton  of  calcium  carbide  requires  5,889  H. P. 
hours,  or  conversely,  for  each  H.P.  day  of  24  hours,  4-1  kgs. 
of  calcium  carbide  may  be  formed." 

The  Progressive  Age,  in  1896,  deputed  Messrs.  Houston, 
Kennelley,  and  Kinnicutt  to  carry  out  some  experiments 
in  carbide  manufacture  on  a  commercial  scale  at  Spray, 
N.  Carolina,  with  a  view  to  determining  the  actual  cost  of 
production. 

The  plant  was  of  300  H.P.  and  the  current  was  delivered 
at  the  furnace  terminals  at  an  E.M.F.  of  100  volts.  There 
were  two  furnaces,  each  with  a  hearth  area  3  ft.  by  2  ft. 
6  in.,  the  hearth,  and  fixed  electrode,  consisting  of  a  carbon 
plate,  8  in.  thick,  supported  on  an  iron  base  plate.  The 

101 


ELECTRIC    FURNACES    AND 

upper  electrode  was  vertically  adjustable,  and  .  consisted 
of  a  composite  carbon  block,  12  in.  by  8  by  3  :  it  was 
consumed  at  the  rate  of  ^  in.  per  hour.  The  charge  con- 
sisted of  the  usual  coke  and  lime,  containing  37  per  cent, 
carbon,  and  52  per  cent,  lime,  respectively.  The  furnaces 
were  started  by  striking  an  arc  between  the  upper  electrode, 
and  a  small  quantity  of  the  raw  charge  placed  upon  the 
hearth.  The  upper  electrode  was  gradually  raised,  and 
fresh  material  added,  until  a  pyramidal  mass  of  carbide 
was  built  up,  equal,  or  nearly  so,  to  the  cubic  capacity  of 
the  furnace. 

Two  runs  were  made,  the  weight  of  raw  material  treated 
in  each  case  being  900  kgs.,  whilst  an  output  of  about 
90  kgs.  of  calcium  carbide  resulted  from  each.  The  con- 
sumption of  energy  was,  in  the  first  instance,  193-1  H.P. 
for  three  hours,  or  579-3  h.p.  hours  =  432 k.w.  hours;  and, 
in  the  second,  195-3  H.P.  for  2  hours  40  minutes,  or  520-8 
h.p.  hours  =388-5  k.w.  hours. 

The  respective  yields  were  thus  3-75  kgs.  of  80  to  85  per 
cent,  carbide  per  h.p.  per  24  hours,  and  4-15  kgs.  for  the 
same  expenditure  of  power  respectively. 

Many  and  varied  are  the  figures  relating  to  the  energy 
required  for  the  production  of  calcium  carbide,  not  only  on 
a  commercial  scale,  but  also  from  a  theoretical  standpoint 
based  on  calculations  involving  thermal  data  regarding 
the  component  materials  themselves.  In  this  connexion, 
Mr.  J.  B.  C.  Kershaw,  F.I.C.,  contributed  a  very  interesting 
series  of  articles  which  first  appeared  in  the  Electrician, 
November  23,  1900. 

Dealing,  primarily,  with  the  theoretical  side  of  the  ques- 
tion, the  following  table,  excerpted  from  the  Electrician 
of  that  date,  gives  his  figures,  in  tabular  form,  as  gleaned 
from  various  authorities  on  the  subject  of  calcium  carbide 
manufacture,  the  actual  references  being  quoted  in  the 
original  article — 


102 


Of 


THEIR    INDUSTRIAL   APPLICATIONS 


AUTHORITY. 
Sieber 
Addicks 
Bredel 
Wolff 
Pictet  . 
Haber  . 
Gin       . 
Lewes  . 
Allen 


KILOWATT  HOURS. 
1,523 
1,941 
1,960 
2,043 
2,640 
2,670 
3,069 
3,290 
3,293 


In  the  above  table,  the  figures  represent  the  kilowatt 
hours  theoretically  necessary  to  produce  one  metric  ton 
(2,204  Ibs.)  of  calcium  carbide  containing  80  per  cent, 
carbide. 

As  Mr.  Kershaw  observes,  there  is  a  wide  disparity  be- 
tween the  figures  quoted  above,  which  is  in  the  main  due 
to  the  fact  that  no  allowance  has  been  made  for  waste  of 
material  in  the  furnace,  nor  for  the  heat  required  to  raise 
the  temperature  of  the  charge,  in  the  first  instance,  to  that 
at  which  the  actual  carbide  formation  takes  place. 

In  the  course  of  his  article,  the  Author  discusses  the 
various  possible  sources  of  error,  and,  in  summing  up, 
decides  in  favour  of  the  calculation  made  by  M.  Gin,  and 
published  in  UEclairage  Electrique,  May  6,  1899. 

The  following  is  the  reasoning  referred  to — 

"  The  temperature  of  the  reaction  is  taken  as  3,300°C.  = 
5,972°F.,  and  the  following  formulae  are  used  for  calculating 
the  specific  heats  of  the  carbon  and  lime  at  that  tempera- 
ture— 

Carbon  (atomic  heat)  ...       .     4-26 +0-00072t. 

Lime  (gramme  molecule)       .          .          .      11-4+0-OOlt. 

Using  these  data,  the  following  figures  are  obtained  for 
the  production  of  the  gramme  molecule  of  calcium  carbide — 

Heat  necessary  to  raise  56  grammes  of 

limeto3,300°C 

Heat  necessary  to  raise  36  grammes  of 

carbon  to  3,300°C. 


Heat  necessary  to  split  up  56  grammes 
lime  into  Ca  and  O 


43,060  Calories. 
53,940 
145,000 


Total 


.     242,000 


103 


ELECTRIC   FURNACES    AND 

Less — 

Heat    produced    by    formation  of  28 

grammes  of  CO      .          .  .          .        26,100  Calories 

Heat    produced    by    formation  of  64 

grammes  of  CaC2  .  .          .         3,900        „ 

Net  Heat  required          .          .     212,000 

212,000  Calories  =  245*5  watt  hours  electrical  energy 
=  3,837  k.w.  hours  per  ton  of  carbide. 

Mr.  Kershaw  next  proceeds  to  deal  with  the  various 
experimental  and  estimated  yields  of  carbide,  the  results 
of  which  are  embodied  in  the  following  table — 


AUTHORITY. 

Lewes  .          *  • 

Korda 

Houston  and  Kennelly 

Bullier 

Liebetanz 

Wolff 


KILOWATT  HOURS. 

.  4,105 

.  4,380 

.  4,393 

.  4,470 

.  4,800 

.  5,111 

.  6,514 


The  figures  in  the  above  table  represent  the  kilowatt 
hours  necessary  to  produce  one  metric  ton  (2,204  Ibs.)  of 
calcium,  containing  80  per  cent,  carbide,  as  determined 
by  actual  experiment,  and  estimates  based  on  the  results 
of  the  same. 

Finally,  in  Table  No.  3,  below,  Mr.  Kershaw  gives  us  the 
results  obtained  in  actual  practice — 


AUTHORITY. 


*  Lewes  . 
*Keller 
*Carlson 
Patten 
Borchers 
Keller  . 
Lewes 
Haber 
Pierard 
Nikolai 
Carlson 
Haber 


KILOWATT  HOURS. 

.  3,576 

.  3,788 

.  3,871 

.  4,104 

.  4,105 

.  4,157 

.  4,291 

.  4,351 

.  4,470 

,  4,920 

.  5,066 

.  5,616 

.  5,960 


104 


THEIR    INDUSTRIAL   APPLICATIONS 

The  above  figures  represent  the  kilowatt  hours  necessary 
to  produce  one  metric  ton  (2,204  Ibs.)  of  calcium  carbide, 
containing  80  per  cent,  carbide,  in  actual  commercial 
practice. 

Summing  up  these  various  data,  Mr.  Kershaw  finally 
decides  in  favour  of  those  marked  with  an  asterisk  as  being 
the  most  reliable.  They  represent  results  obtained  with 
the  Deutsche  Gold  und  Silberscheide  Anstalt  form  of  fur- 
nace ;  the  Willson  furnace,  as  used  at  Foyers  ;  and  the 
Gin  and  Leleux  production,  in  use  at  Meran,  in  Austria. 
These  three  types  are  described  elsewhere,  and  may  be 
taken  as  representing  three  of  the  most  efficient  carbide 
furnaces  then  in  practical  use. 

Cost  of  Calcium  Carbide  Manufacture. — The  cost  of 
calcium  carbide  manufacture  must  necessarily  be  largely 
governed  by  local  conditions,  source  of  power,  cost  of  raw 
materials,  etc.,  so  that  it  is  impossible  to  formulate  any 
hard  and  fast  rule  on  the  subject. 

Some  interesting  figures,  from  various  sources,  are 
assembled  in  the  form  of  a  statistical  article  on  the  progress 
of  the  industry  by  Kershaw,  in  the  Electrical  Review,  Sep- 
tember 22,  1899. 

At  Lourdes,  in  the  Hte.  Pyrenees,  the  cost  is  estimated 
at  about  £12  per  ton.  In  Switzerland,  at  that  time,  car- 
bide was  selling  at  £14  per  ton,  and,  in  Paris,  at  £19. 

At  Meran,  in  the  Austrian  Tyrol,  it  was  estimated  to  cost 
£7  5s.  per  ton,  f.o.r.,  and  that  after  allowing  for  interest 
on  capital  and  depreciation  of  plant. 

At  Niagara,  in  1899,  it  was  estimated  that  carbide  could 
be  produced  at  from  £7  5s.  to  £8  per  ton. 

Liebetanz,  in  his  paper  before  the  Buda  Pesth  Congress, 
estimates  the  cost  of  production  with  steam  power  at 
£11  145.  per  ton,  and  with  water  power  at  £8  18s. 

According  to  Carl  Hering  (ISEclairage  Electrique)  it 
requires,  theoretically,  1,900  Ibs.  of  lime,  and  1,230  Ibs. 
of  carbon  to  produce  one  ton  of  calcium  carbide  ;  in  actual 

105 


ELECTRIC   FURNACES    AND 

practice,  2,050  Ibs.  of  lime,  and  1,420  Ibs.  of  carbon  are 
necessary.  These  figures  apply  particularly  to  the  carbide 
factory  at  Meran,  in  Austria,  where  the  cost  of  lime,  per 
ton,  was  then  about  16$.,  and  of  carbon,  32s. 

One  electrode  suffices  for  ten  tons  of  carbide,  and  costs 
£6  12s.  or  approximately  13s.  per  ton. 

The  electrical  energy  required  per  ton  of  carbide  produced 
was  6,400  h.p.  hours,  which,  at  £2  per  E.H.P.  year,  works 
out  at  a  little  above  £1  16s.  per  ton. 

Accessory  machinery,  losses,  etc.,  account  for  about 
200  H.P.,  or  4s.  per  ton,  the  output  being  6-5  tons  per  diem. 

Labour,  at  3s.  to  3s.  4d.  per  day,  amounts  to  15s.  per  ton. 
Amortisation  £1  per  ton,  and  general  expenses  £1  per  ton  ; 
maintainance  of  plant,  6s.  per  ton.  Total  cost,  at  Meran, 
£7  5s.  per  ton. 


106 


THEIR    INDUSTRIAL    APPLICATIONS 


SECTION   V 

IRON  AND  STEEL  PRODUCTION  IN  THE  ELECTRIC  FURNACE 

Introductory. — M.  Keller,  of  the  electro-metallurgical 
firm,  Keller,  Leleux  and  Co.,  France,  in  a  paper  before  the 
Iron  and  Steel  Institute,  1903,  states  the  conditions  under 
which  electrical  reduction  processes  may  be  economically 
adopted  ;  they  are  as  follows — 

"  Although  the  reduction  of  iron  ores  by  electricity  has 
formed  the  subject  of  a  practical  study  by  the  Author,  the 
results  of  which  will  be  described  further  on,  it  may  be 
stated  at  once  that  the  employment  of  electricity  as  a 
reducing  agent  is  only  practicable  from  an  economic  point 
of  view  :  first,  when  it  is  a  question  of  manufacturing  special 
qualities  of  iron,  from  pure  ore,  delivered  at  the  works 
on  favourable  terms.  Secondly,  when  it  is  desired  to  foster 
an  iron  and  steel  industry  in  a  country  hitherto  undeveloped 
in  this  respect,  into  which  all  the  coal  must  be  imported, 
where  iron  ore  of  good  quality  abounds,  and  where  natural 
sources  of  power  are  available  in  the  immediate  neighbour- 
hood of  the  ore  deposits. 

"  The  Author  has  determined,  experimentally,  that  one 
k.w.  year,  utilized  in  an  electric  reducing  furnace,  is  capable 
of  yielding  about  four  tons  of  steel-making  pig-iron.  In 
a  general  way,  therefore,  the  reduction  of  iron  ore  by 
electricity  in  a  country  possessing  metallurgical  works 
and  equally  good  conditions  of  transport  throughout,  is 
only  theoretically  practicable  if  the  ore  can  be  obtained 
on  equal  terms,  and  if  the  cost  of  the  kilowatt  year  does  not 

107 


ELECTRIC    FURNACES    AND 

exceed  £1  55.  6d.  It  must  be  borne  in  mind,  however, 
that  the  scale  of  production  of  an  electric  furnace  is  less 
than  that  of  blast  furnaces,  and  that,  on  this  account, 
establishments  equipped  for  electric  working  would  be 
of  less  capacity  ;  the  working  expenses  being  also  pro- 
portionately higher,  it  does  not  appear  as  if  the  reduction 
of  iron  ores,  so  far  as  the  smelting  of  ordinary  pig  is  con- 
cerned, will  ever  enter  the  sphere  of  practice  in  any  European 
hydro-electric  works." 

The  advantages  of  the  electric  reduction  process  are  thus 
detailed  by  the  same  authority — 

"  A  high  degree  of  purity  can  be  reached  by  the  electric 
method  of  production,  owing  to  the  method  of  generating 
the  heat,  which  enables  the  action  of  the  fuel  to  be  limited 
strictly  to  that  of  a  reducing  agent.  By  this  means  the 
action  of  the  sulphurous  gases  is,  to  a  great  extent,  avoided  ; 
and,  since  the  quantity  of  coke  required  per  ton  of  iron  is 
so  small,  the  very  best  qualities  can  be  utilized  for  the 
purpose.  It  is  therefore  possible,  with  good  ore,  to  obtain 
a  pig-iron  which  will  compare  in  purity  with  Swedish  iron. 
A  further  advantage  consists  in  the  higher  temperature  of 
working,  which  the  use  of  electricity  permits,  without, 
however,  causing  an  excess  of  carbon  in  the  material.  It 
is  also  possible,  in  consequence  of  the  hot  working,  to  form 
slags  of  ultra-basic  character." 

In  steel  production,  on  the  other  hand,  the  cost  of  the 
electrical  energy  is  a  secondary  consideration.  In  melting 
and  fining  one  ton  of  steel  produced  from  scrap  iron  and 
steel,  M.  Keller  estimates  that  about  1-10  k.w.  year  is  neces- 
sary, and,  even  using  steam  as  the  primary  source  of  power, 
the  cost  of  energy  will  only  amount  to  about  £1  12<s.  per 
ton  of  steel. 

According  to  Heroult,  2,500  tons  of  steel  have  been 
already  produced  in  the  electric  furnace,  whilst  plant, 
with  an  aggregate  capacity  of  400  tons  of  steel  per  day, 
is  in  operation.. 

1 08 


THEIR    INDUSTRIAL    APPLICATIONS 

In  both  the  Heroult  and  Keller  electric  furnace  steel 
processes,  the  heating  arcs  are  struck  between  the  metallic 
charge  and  the  electrodes.  The  Heroult  furnace  is  in  opera- 
tion at  La  Praz,  and  the  Keller  at  Li  vet,  on  the  Bomanche. 
As  will  be  seen  from  the  above,  the  cost  of  smelting  iron 
ores  by  electrical  means  is  somewhat  large,  and,  in  the 
present  stage  of  its  development,  can  only  hope  to  com- 
pete with  ordinary  blast  furnace  processes,  in  special  cases, 
as  for  example,  where  power  can  be  had  at  a  comparatively 
low  figure,  whilst  pure  ore  is  plentiful. 

Dr.  H.  Goldschmidt,  who  has  acted  in  the  capacity  of 
inspector,  appointed  by  the  German  Patent  Office  to 
report  on  the  various  electric  smelting  processes,  has  fur- 
nished some  interesting  information  and  data  on  the  sub- 
ject (Zeitschrift  fur  Elektrochemie,  1903). 

With  reference  to  the  earliest  industrial  application  of 
the  electric  furnace  to  smelting  processes,  it  may  be  men- 
tioned that  to  Heroult  belongs  the  honour  of  having  made 
the  pioneer  move,  for,  according  to  Goldschmidt,  he  de- 
livered his  first  car-load  of  steel,  consisting  of  bars  weigh- 
ing 400  kgs.  each,  and  amounting,  in  all,  to  8,890  kgs.,  to 
Messrs.  Schneider  &  Co.,  Creusot,  on  December  28,  1900. 
This  consignment  was  the  product  of  his  electric  furnace 
at  Froges. 

The  electric  furnace  has  hot  been  commercially  applied 
in  America  to  iron  and  steel  manufacture,  but  Europe  has 
been  the  scene  of  many  experimental  and  commercial 
trials,  with  some  of  which  very  successful  results  have 
been  obtained.  This  latter  fact,  combined  with  the  exist- 
ence of  rich  iron  deposits  in  Canada,  a  country  in  which 
water  power  is  abundant,  has  prompted  the  Canadian 
Government  to  appoint  a  Commission  to  visit  Europe, 
and  study  the  possibilities  of  electric  smelting,  ore  reduction, 
and  steel  manufacture,  with  a  view  to  its  industrial  develop- 
ment in  Canada. 

Sweden,   France,   and  Italy  are  the  principal  countries 

109 


ELECTRIC    FURNACES    AND 

to  be  visited  by  this  Commission,  which,  at  the  time  of 
writing,  is  actually  engaged  upon  its  work  of  investigation. 
Some  valuable  information  should  be  the  outcome  of 
this  enterprise,  and  the  advent  of  the  official  report  will 
doubtless  be  awaited  with  interest  by  metallurgists  in 
general. 

The  resistance  furnace,  with  carbon  core,  has,  until 
comparatively  recently,  been  commercially  inapplicable 
to  the  smelting  or  reduction  of  non- volatile  metals,  for  the 
simple  reason  that  the  mere  presence  of  carbon  in  the 
core  has  led  to  the  formation  of  a  carbide  by  reaction  with 
the  metal  liberated  from  the  ore. 

Acheson  has,  however,  surmounted  this  obstacle  by 
protecting  the  carbon  core  from  contact  with  the  charge 
of  metallic  ore  by  an  impervious  sheath,  e.g.,  carborundum. 
The  arrangement  is  very  simple  ;  around  the  carbon  or 
granular  coke  core  of  an  ordinary  resistance  furnace  of 
the  well-known  Acheson  type  is  packed  either  a  quantity 
of  carborundum  crystals,  already  formed,  or  sufficient 
silica  and  carbon,  mixed  in  the  correct  proportions,  to  form 
carborundum.  Outside  this,  again,  is  placed  the  mass 
of  ore  to  be  reduced.  In  action,  the  carborundum  forms 
a  coherent  impermeable  sheath,  which  is  self-supporting, 
and  maintains  its  position  around  the  core,  even  after  the 
encircling  charge  has  fallen  away  from  it  by  virtue  of  the 
reduction  taking  place.  With  the  aid  of  this  protecting 
sheath,  Acheson  has  succeeded  in  effecting  the  direct 
reduction  of  silicon  and  aluminium  in  the  electric  furnace. 

Processes. — In  connexion  with  the  various  thermo- 
electric processes,  experimental  and  otherwise,  for  the 
manufacture  of  steel,  the  following  table,  containing  results 
and  data  furnished  by  Goldschmidt,  of  Essen,  at  the  Fifth 
International  Congress  of  Applied  Chemistry,  may  prove 
of  interest. 


no 


THEIR    INDUSTRIAL   APPLICATIONS 


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III 


ELECTRIC   FURNACES    AND 

According  to  Ruthenberg,  the  production  of  one  ton  of 
metallic  iron  requires,  by  the 

Stassano  process  ....  3,000  h.p.  hours. 

De  Laval       „  ....  3,500     „ 

Rossi  „  ....  4,800     „ 

Ruthenberg   „  ....         500  k.w.      „ 

Comparing  the  economy  of  the  blast  furnace  process 
with  that  of  the  electric  furnace,  Ruthenberg  points  out 
that  a  ton  of  coke  is  required  for  the  production  of  one  ton 
of  pig-iron,  of  which  only  a  little  more  than  150  kgs.  are 
actually  required  for  the  reduction  of  the  ore,  the  remainder 
being  necessary  to  melt  the  reduced  iron,  and,  incidentally, 
to  form  cinder,  whilst  no  inconsiderable  portion  is  lost  or 
wasted  in  the  form  of  combustible  gas. 

One  of  the  earliest  attempts  to  apply  the  electric  furnace 
to  smelting  operations,  was  that  made  in  1892  by  De  Laval, 
of  Stockholm,  his  furnace  being  of  the  resistance  type,  but 
differing  from  most  others  of  a  like  kind,  in  that  the  core 
consisted  of  fused  magnetite.  The  mass  of  this  latter, 
which  constituted  a  molten  bath,  was  disposed  between,  but 
separated  from,  two  pockets  of  molten  iron,  which  served 
the  double  purpose  of  terminal  electrodes  and  receptacles 
for  the  reduced  metal  which  found  its  way  into  them 
during  the  process,  and  was  constantly  tapped  from  them 
in  order  to  ensure  a  constant  level. 

An  alternating  current  was  used  with  this  device,  the 
ores  to  be  smelted,  mixed  with  the  necessary  proportion  of 
carbon,  being  fed  into  the  bath  of  molten  magnetite,  where 
they  underwent  reduction  by  the  heat  generated  electri- 
cally in  the  molten  mass. 

The  Gin  furnace  for  steel  manufacture  is  based  on  the 
same  resistance  principle,  and  is  probably  one  of  the  simplest 
in  point  of  application. 

It  comprises  a  long  trough,  shown  at  T,  in  transverse 
section,  Fig.  27,  lined  with  refractory  material  R.  This 

112 


THEIR    INDUSTRIAL   APPLICATIONS 

trough  is  filled  with  fused  cast  iron  F,  which,  in  addition 
to  being  the  material  under  treatment,  also  constitutes 
the  heating  resistance  column.  The  terminal  connexions 


FIG.  27. 

through  which  current  is  conveyed  to  the  molten  column 
are  large  blocks  of  steel,  kept  cool  by  internal  water  cir- 
culation, and  also  by  virtue  of  their  greater  cross-section. 

The  inconvenience  attendant  on  so  unwieldy  a  construc- 
tion as  would  be  entailed  by  arranging  the  resistance  channel 
or  furnace  hearth,  in  one  straight  length,  is  eliminated  by 
doubling  it  back  upon  itself  several  times  in  zig-zag  fashion, 
as  shown  at  E,  Fig.  27,  where  t  is  the  trough,  and  e  e  the 
terminal  electrode  blocks.  Thus  constituted,  the  furnace 
may  be  likened  to  a  huge  incandescent  electric  lamp  fila- 
ment ;  it  is  mounted,  for  portability,  on  a  trolley,  which 
can  be  run  in  and  out  of  an  arched  furnace,  for  the  recep- 
tion of  the  charge  of  molten  pig-iron,  which  has  been 
primarily  fused  in  the  latter. 

There  are  two  distinct  methods  of  manufacturing  steel 
by  the  Gin  process  known  respectively  as  the  "  dilution  " 
method,  and  the  "  ore  process."  They  are  employed 
either  independently,  or  in  combination.  The  former  is 
very  simple,  and  consists  in  adding  a  calculated  percentage 
of  scrap  iron  to  the  molten  mass,  in  which  it  dissolves, 
followed  by  the  speedy  diffusion  of  the  carbon  throughout 
the  mass,  and  its  consequent  conversion  into  steel. 

The  "  ore  process  "  entails  the  addition  of  iron  oxide  to 
the  mass,  the  oxygen  of  which  assists  in  the  elimination  of 
undesirable  impurities. 

M.  Keller's  electric  blast  furnace  for  the  reduction  of 

113  i 


ELECTRIC   FURNACES   AND 

iron  ores  resembles  an  ordinary  blast  furnace  in  general 
appearance,  its  hearth  being  surmounted  by  a  shaft  of 
refractory  brick  for  the  reception  of  the  ores,  flux,  and 
reducing  materials,  which  are  fed  in  at  the  top  through  a 
gas-tight  valve. 

The  electrodes  are  vertical,  and  laterally  disposed,  each 
one  being  capable  of  independent  adjustment,  which  enables 
their  several  heating  effects  to  be  equalized  by  means  of  an 
ammeter  included  in  each  circuit. 

There  are  at  least  four  of  these  electrodes  to  a  furnace, 
and  any  one  of  them  can  be  removed  and  replaced  without 
stopping  the  run.  At  the  commencement  of  a  run  the 
current  is  switched  on,  and  the  furnace  chamber  filled  with 
raw  materials.  Fusion  commences  at  the  bottom,  in  the 
neighbourhood  of  the  hearth,  but  soon  extends  upwards 
throughout  the  entire  mass,  the  resultant  gases  being  led 
off  and  burnt,  to  dry  and  preheat  the  ores. 

The  steel  fining  furnace  is  placed  at  a  lower  level,  its 
inlet  being  just  below  the  tap-hole  of  the  blast  furnace, 
so  that  the  reduced  iron  can  flow  into  it.  Two  vertical 
electrodes  are  used,  which  just  establish  contact  with  the 
surface  of  the  slag,  but  do  not  penetrate  to  any  appre- 
ciable depth. 

The  E.M.F.  at  the  terminals  of  the  reducing  furnace  is 
25-30  volts,  and  of  the  steel  furnace,  50-75  volts. 

M.  Keller  estimates  that  an  electro-metallurgical  works, 
with  10,000  H.P.  available,  could  produce,  by  his  process, 
60  tons  of  steel  per  diem,  of  which  50  tons  would  accrue 
from  55  per  cent,  ore,  and  the  remaining  ten  tons  from  the 
fusion  of  scrap. 

The  cost  of  the  process,  assuming  a  k.w.  year  of  8,400 
hours  to  run  into  £2,  would  be  from  £3  125.  to  £4  per  ton 
of  steel,  exclusive  of  royalties,  payable  on  the  patent 
rights  ;  the  electrical  energy  would  be  responsible  for 
only  135.  3d.  of  the  above  total  cost. 

The  electrical  manufacture  of  steel  by  the  Keller  process, 

114 


THEIR   INDUSTRIAL   APPLICATIONS 

as  carried  on  at  Kerrouse,  France,  has  proved  highly  suc- 
cessful. All  varieties  of  iron  ore  have  been  electrically 
fused  and  treated.  Practical  trials  have  demonstrated 
that  for  the  manufacture  of  one  ton  of  steel  from  ordinary 
ores,  electrical  energy  to  the  extent  of  2,800  k.w.  hours,  or 
3,800  e.h.p.  hours  is  required. 

The  total  cost  of  manufacture,  including  electrodes,  coke, 
ore,  refining  materials,  etc.,  and  general  expenses,  was 
found  to  be  from  £3  15s.  to  £4. 

The  ultimate  disposition  at  Kerrouse  will  consist  of  a 
battery  of  electric  furnaces,  served  by  one  portable  refining 
furnace,  which,  in  the  form  of  a  large  ladle,  is  placed  before 
each  furnace  in  turn,  and  the  electrodes  lowered  into  its 
contents,  tapped  from  the  reducing  furnaces. 

The  Simon  electric  furnace,  for  smelting  iron  and  other 
ores,  consists  of  a  movable  truck  hearth,  which  carries  the 
negative  electrode,  consisting  of  horizontal  carbon  blocks 
embedded  in  a  layer  of  powdered  ferro- manganese.  Small 
priming  blocks  of  carbon  rest  on  the  upper  surfaces  of 
these,  and  serve  as  a  temporary  bridge  between  the  cathode 
and  the  vertical  anodes,  which  are  similar  carbon  blocks 
embedded  in  a  compressed  mass  of  slag,  tar,  and  resin. 
The  upper  electrodes  slide  vertically  in  a  frame,  and  the 
active  hearth  of  the  furnace  is  enclosed. 

The  electrical  process  of  iron  smelting  and  steel  produc- 
tion, originally  devised  by  M.  Henri  Harmet,  consisted  of 
three  distinct  operations,  viz.,  the  reduction  of  the  ore  ; 
the  fusion  of  the  ore  ;  and,  finally,  the  refining  of  the 
resultant  metal.  In  a  later  patent,  the  order  of  the  first 
two  processes  has  been  reversed,  the  ores  being  first  fused 
and  then  reduced. 

Electrical  heat  is  largely  employed  in  the  process,  but  is 
supplemented  by  the  heat  of  combustion  of  the  gases  pro- 
duced in  the  intermediate,  or  reduction  chamber,  which  are 
mixed  with  air,  and  forced,  under  pressure,  into  the  lower 
portion  of  the  first,  or  fusion  chamber. 


ELECTRIC   FURNACES   AND 

The  three  furnaces  are  arranged  with  their  hearths 
sloping  in  cascade,  so  that  the  fused  matter  may  run  from 
the  fusion  chamber  into  the  reduction  furnace,  and  the 
resultant  metal  from  the  latter  into  the  refining  oven. 

In  the  fusion  chamber,  the  electrodes  are  placed  at  the 
bottom,  or  hearth,  whilst  in  the  intermediate,  or  reduction 
furnace,  they  are  vertically  arranged,  with  their  lower 
extremities  touching,  but  not  penetrating,  the  upper  layer 
of  slag. 

The  coke  is  fed  into  the  reducing  furnace  down  a  vertical 
tower,  or  cylindrical  structure,  resembling  an  ordinary 
blast  furnace,  emerging  finally,  upon  the  sloping  hearth, 
at  a  point  just  in  advance  of  the  tapping  holes  leading  to 
the  refining  oven ;  it  thus  interposes  an  incandescent 
screen,  through  which  the  molten  metal  and  slag  have  per- 
force to  filter,  before  passing  into  the  latter. 

The  initially  smelted  metal  forms  a  thin  layer  on  the 
hearth  of  the  reducing  chamber,  upon  which  floats  the  slag, 
and  also  a  coating  of  coke,  detached  from  the  main  column. 
The  molten  ores  from  the  fusion  chamber,  flow  on  to  this 
mixture  of  coke  and  slag,  and  in  the  intense  heat  generated 
by  the  electric  current  are  reduced,  as  in  an  ordinary 
blast  furnace,  passing  through  the  descending  screen 
of  heated  coke,  before  finally  reaching  the  refining  oven, 
which  operates  on  a  similar  principle  to  that  of  the 
Martin  type. 

A  later  patent  taken  out  by  M.  Harmet  covers  an  electric 
blast  furnace  with  a  lower  "  fusion  zone,"  and  an  upper 
"  reduction  zone."  The  electrodes  pass  through  the  walls, 
and  the  excess  heat,  generated  in  process  of  fusion,  is 
utilized  for  purposes  of  reduction.  To  this  end,  the  gases 
from  the  top  of  the  furnace  are  collected,  and  led  off  by 
pipes,  to  a  fan  or  blower,  which  re-introduces  them,  under 
pressure,  into  the  furnace,  in  the  neighbourhood  of  the 
fusion  centre.  They  again  pass  upward,  carrying  with 
them  the  excess  heat  energy  into  the  reduction  zone. 

116 


THEIR    INDUSTRIAL    APPLICATIONS 


The  gases,  on  coming  into  contact  with  the  incandescent 
coke,  are  converted  into  carbon  monoxide,  which  effects 
the  necessary  reduction  of  the  descending  charge  as  it 
diffuses  upwards.  It  will  be  seen  from  this  that  the  opera- 
tion is  continuous. 

A  patent  granted  to  Prof.  W.  S.  Franklin,  of  Lehigh 
University,  towards  the  latter 
end  of  1903,  covers  a  somewhat 
ingenious  form  of  electric  fur- 
nace construction,  primarily 
intended  for  the  reduction  of 
iron  ore,  but  also  applicable  to 
the  manufacture  of  glass.  The 
furnace,  illustrated  in  Fig.  28, 
consists  of  a  pear-shaped  de- 
pression, or  hearth,  in  a  refrac- 
tory base  B,  extending  up- 
wards into  a  funnel-shaped 
opening  or  feed  hopper. 

The  novelty  of  the  design 
lies  in  the  construction  of  the 
upper  electrode  E,  which  may  T\ 
be  of  carbon,  or  metal,  ac- 
cording to  circumstances.  Its 
outer  surface  is  furnished  with 
downwardly  inclined  teeth,  t  t 

like  those  of  a  saw,  whilst  it  is  clamped,  at  its  upper 
extremity,  to  the  moving  member  of  an  eccentric  or  re- 
ciprocating motion  R. 

The  raw  charge  is  fed  into  the  funnel-shaped  mouth  H, 
around  this  central  electrode,  which  latter,  by  its  vertical 
movement,  carries  it  down  into  the  furnace  proper,  the 
return  stroke,  owing  to  the  slope  of  the  teeth  t  t,  moving 
the  charge  in  the  hopper  but  little,  if  at  all.  In  this  manner, 
a  constant  feed  is  secured. 

When  applied  to  the  reduction  of  iron  ores,  a  layer  of 

117 


FIG.  28. 


ELECTRIC   FURNACES    AND 

carbon  C  is  placed  at  the  lower  portion  of  the  hearth, 
electrical  connexion  with  it  being  secured  by  an  iron  rod, 
passing  through  the  refractory  wall.  Over  this  is  packed 
a  filling  of  slag,  and  the  current  turned  on.  The  resultant 
heat  is  regulated  by  the  height  of  the  upper  electrode  ; 
if  the  latter  dips  into  the  molten  slag,  the  furnace  operates 
on  the  resistance  principle,  and  the  heating  effect  is  moderate  ; 
if,  however,  it  be  raised  out  of  contact  with  the  surface 
of  the  slag,  an  arc  is  struck  between  the  two,  and  the  tem- 
perature augmented. 

As  the  ore  descends  on  to  the  surface  of  the  molten  slag, 
it  melts,  and  the  metal  filters  through  to  the  lower  portion 
of  the  hearth,  whence  it  is  drawn  off  by  way  of  the  tap- 
hole  T.  A  similar  opening  S,  at  a  higher  elevation,  pro- 
vides for  the  removal  of  the  superfluous  slag. 

When  utilized  for  the  electrical  manufacture  of  glass, 
an  initial  charge  of  that  substance  is  given  to  the  furnace, 
in  order  to  start  the  action,  after  which  the  raw  mixture 
is  fed  in  as  before,  the  resultant  glass  being  drawn  off  in 
a  molten  condition  at  the  lower  tap-hole  T. 

A  simple  and  comprehensive  patent,  taken  out  in  1899 
by  Dr.  Borchers,  relates  to  resistance  furnace  methods 
of  smelting  and  ore  reduction,  in  which  carbon  is  employed 
as  the  reducing  agent.  The  process  consists  in  packing 
the  whole  of  the  carbon  employed  in  the  reaction  between 
two  electrodes,  to  act  as  a  heating  resistance  core,  and 
surrounding  the  mass  with  an  encircling  filling  of  the  ore 
or  substance  to  be  acted  upon.  No  preliminary  mixing 
of  the  two  ingredients  is  necessary  in  this  method,  which 
is  closely  allied  to  that  of  Dr.  Borchers,  described  under 
the  section  dealing  with  carbide  furnaces. 

In  1901  a  French  patent  was  taken  out  by  the  Societe 
Electrometallurgique  Fran9aise  on  an  arc  furnace  for  the 
manufacture  of  all  varieties  of  iron  and  steel  in  one  opera- 
tion, by  the  direct  treatment  of  specific  mixtures  of  iron 
ore,  carbon,  and  such  other  ingredients  as  are  determined 
by  the  nature  of  the  product  required. 

118 


THEIR    INDUSTRIAL    APPLICATIONS 

The  furnace  construction  is  very  simple,  consisting  of 
a  refractory  crucible,  provided  with  a  domed  cover  of 
loose  fire-bricks,  which  can  be  removed  for  charging  pur- 
poses, and  through  which  pass  two  similar  vertical  elec- 
trodes. These  latter  do  not  extend  to  the  bottom  of  the 
crucible,  but  only  to  a  level  with  the  upper  tapping-hole, 
provided  for  the  removal  of  the  slag  formed  in  the  smelting 
process. 

The  molten  metal  collects  at  the  bottom  of  the  crucible 
below  the  level  of,  and  consequently  out  of  contact  with, 
the  electrodes,  and  is  drawn  off  at  a  separate  tapping-hole, 
situated  at  the  lowest  point  of  the  hearth. 

The  principle  of  the  arc  smelting  furnace,  devised  by 
Dr.  F.  C.  Weber,  consists  in  allowing  the  raw  material, 
or  ore,  to  fall  vertically  through  the  intense  heat  zone  pro- 
duced by  a  number  of  arcs,  into  a  suitable  receptacle  placed 
below. 

The  furnace  comprises  a  tower-like  structure,  with  the 
usual  feed  hopper  at  its  upper  extremity,  around  the  point 
of  entry  of  which,  into  the  furnace,  is  arranged  an  outer  per- 
forated jacket,  to  permit  the  escape  of  the  combustion  gases. 

Below,  the  structure  broadens  out  into  a  species  of  tunnel 
for  the  reception  of  a  removable  truck  to  contain  the  molten 
metal  smelted  by  the  arcs.  The  electrodes  for  these  latter 
pass  through  the  side  walls  of  the  furnace  at  varying  heights, 
just  above  the  receiving  chamber,  being  arranged  in  equal 
horizontal  rows  of  opposing  carbons.  Several  of  these 
rows  are  arranged,  one  above  the  other,  constituting,  when 
active,  a  perfect  sheet,  or  bank  of  arcs,  through  which  the 
raw  material  has  to  pass  in  falling  to  the  base  of  the  furnace. 

Each  arc  is  given  independent  control,  so  that  its  in- 
tensity and  consequent  heating  effect  may  be  regulated 
at  the  will  of  the  operator,  the  usual  procedure  being  to 
graduate  them  in  such  manner  that  the  most  intense  heat 
is  at  the  top,  where  the  charge  first  comes  into^contact 
with  them. 

119 


ELECTRIC    FURNACES    AND 

To  prevent  current  leakage  between  the  electrodes  other 
than  through  the  legitimate  path  of  the  arc,  they  are  passed 
through  the  furnace  walls  in  such  directions  as  to  take  the 
longest  possible  path,  viz.  at  an  angle  to  both  horizontal 
and  vertical  planes. 

A  convenient  arc  furnace  for  the  reduction  of  metallic 
ores,  manufacture  of  steel,  etc.,  has  been  devised  by  M. 
Paul  Heroult.  It  involves  the  production  of  two  arcs 
in  series,  or  may,  if  the  electrodes  are  submerged  in  the 
raw  material  to  be  treated,  be  regarded  as  a  resistance 
furnace,  in  which  the  conducting  path  is  constituted  by 
an  upper  layer  of  the  unconverted  charge. 

In  general  principle  it  is  extremely  simple,  comprising 
an  open  crucible  with  a  refractory  lining,  provided  with 
the  necessary  tapping  holes,  and  two  similar  vertical  elec- 
trodes, between  the  respective  extremities  of  which,  and 
the  surface  of  the  conducting  charge,  the  two  arcs  are  struck. 

The  electrodes  are  mounted  in  massive  holders  attached 
to  screwed  stems  permitting  vertical  adjustment,  means 
for  which  are  provided  in  the  shape  of  bevel  gear,  and 
hand- wheels,  mounted  on  swinging  brackets,  attached  to 
suitable  supports  on  either  side  of  the  crucible.  Two 
separate  voltmeters,  connected  between  the  two  electrodes 
and  the  molten  mass  under  treatment,  respectively,  serve 
as  gauges  of  the  condition  of  the  two  arcs,  whereby  an 
equal  adjustment  can  be  secured. 

One  form  of  the  Heroult  apparatus  for  the  direct  pro- 
duction of  steel  resembles,  in  general  construction,  its 
prototype,  the  Bessemer  converter. 

It  consists  of  a  steel  structure,  shaped  somewhat  like 
a  converter,  and  furnished  with  the  usual  pouring  lip  and 
chimney,  or  gas  outlet.  It  is  lined  throughout  with  re- 
fractory material,  such  as  fire-clay,  and,  rounded  at  its 
base,  to  permit  the  necessary  tilting,  is  mounted  for  con- 
venience on  toothed  rockers,  gearing  with  fixed  rails, 
similarly  cogged. 

120 


THEIR    INDUSTRIAL   APPLICATIONS 

Rigidly  attached  to  the  back  of  the  crucible,  and  thus 
moving  with  it,  are  vertical  supports,  carrying  horizontal 
arms  for  the  reception  of  the  carbon  electrodes,  which  are 
two  in  number,  placed  side  by  side,  the  arcs  being  struck 
in  series,  thus  obviating  the  necessity  for  any  electrical 
connexion  to  the  crucible  itself. 

A  rack  and  pinion  motion,  worked  by  a  hand-wheel,  in 
combination  with  a  clamping  device,  serves  to  adjust  the 
arcs,  and  fix  them  in  position.  The  mode  of  terminal 
attachment  to  the  carbon  electrodes,  which  are  square  in 
section,  is  somewhat  novel,  and  deserves  special  mention. 

The  electrodes  themselves  abut,  through  the  medium 
of  one  face  only,  against  the  plane  surface  of  the  clamp 
attached  to  the  horizontal  supporting  arm.  Around  them 
pass,  loosely,  two  flexible  metal  bands,  also  attached  at 
their  free  extremities  to  the  supporting  arms.  The  con- 
tact between  electrode  and  support  is  made  mechanically 
and  electrically  secure  by  driving  in  copper  wedges  between 
these  bands  and  the  electrode  surfaces,  a  proceeding  which 
not  only  renders  the  whole  construction  rigid,  but  provides 
a  path  of  very  low  electrical  resistance  between  metal  and 
carbon. 

In  larger  models  of  the  above  converter  the  offices  of 
oscillating  the  crucible  and  adjusting  the  carbon  electrodes 
may  be  performed  by  hydraulic  power  instead  of  manually, 
whilst  the  pouring  lip  may  be  extended  into  a  ladle,  per- 
mitting the  resultant  metal  to  be  cast  direct  from  the 
furnace. 

According  to  Goldschmidt,  Heroult  produces  in  his 
furnace  a  tool  steel  of  the  finest  quality  from  a  raw  mixture 
of  cast  iron  and  steel  scrap. 

Each  charge  weighs  approximately  three  tons,  the  elec- 
trodes being  placed  above,  and  an  alternating  current  of 
4,000  amperes  at  60  volts,  employed  in  producing  the  arcs. 

The  percentage  of  impurities  in  the  product  is  estimated 
to  be — 

121 


ELECTRIC    FURNACES    AND 


Sulphur 

Silicon 

Manganese 

Phosphorus 

Carbon 


0-007  per  cent. 
0-003     „        „ 
0-150     „ 
0-003     „ 
0-60  to  1-80  „ 


At  the  time  of  writing  a  plant  is  in  contemplation,  having 
a  capacity  of  600  H.P.,  and  capable  of  dealing  with  15  tons 
of  metal  every  twenty-four  hours,  in  three  operations  of 
the  furnace. 

Fifteen  hundred  tons  of  steel  have  already  been  made 
by  the  Heroult  method  in  France  and  Sweden,  the  process 
being  exploited,  in  the  latter  country,  by  the  Aktiebolaget 
Heroults  Electriska  Stal. 

Heroult's  procedure  in  making  steel  by  the  electric 
furnace  method  consists  in  first  melting  a  charge  of  scrap 
iron,  either  per  se,  or  mixed  with  pig-iron.  The  molten 
mass  is  then  covered  with  an  artificial  slag,  and  subjected 
to  the  action  of  the  arc,  the  sole  object  of  which  is  to  raise 
it  to  the  necessary  temperature.  The  first  slag  is  then 
poured  off,  and  new  fluxes  introduced,  whereby  all  im- 
purities are  removed,  and,  on  adding  carbon  and  other 
ingredients  incidental  to  the  quality  of  steel  required, 
perfect  deoxidation  is  obtained. 

The  works  of  the  Societe  Electrometallurgique  Fran£aise, 
at  La  Praz,  Savoy,  who  manufacture  aluminium,  and  also 
ferro-chrome  and  steel,  by  the  Heroult  process,  utilize  a 
maximum  of  14,000  H.P.  The  machines  recently  installed 
for  electrical  steel  manufacture  are  500  H.P.  single-phase 
alternators,  with  an  output  of  2,750  amperes  at  110  volts, 
and  33  periods  per  second. 

A  later  design  of  electric  furnace,  recently  patented  by 
Heroult,  for  the  production  of  ferro-silicon,  ferro-manganese, 
cast  iron,  etc.,  presents  several  novel  points.  It  is,  how- 
ever, not  an  independent  piece  of  apparatus,  but  is  intended 
to  be  used  in  conjunction  with  a  preparatory  furnace  of 

122 


THEIR    INDUSTRIAL    APPLICATIONS 


the  ordinary  type,  in  which  the  ores  to  be  reduced  are 
primarily  heated  and  softened  before  being  subjected  to 
the  action  of  the  electric  furnace  described  below. 

A  sectional  elevation  is  represented  in  Fig.  29.  It 
works  on  the  resistance  principle,  the  heating  resistance 
taking  the  form  of  a  column  of  coke  C,  which  is  fed  into 
the  furnace  conjointly  with 
the  ores,  and  at  the  same 
time  serves  as  a  reducing 
agent.  A  B  are  the  two 
inlet  or  feed  passages  ;  the 
former  sloped  as  shown  to 
facilitate  the  entry  of  the 
already  softened  ore,  r,  and 
the  latter,  a  vertical  funnel, 
or  chimney,  for  the  coke 
feed. 

The  hearth,  where  the 
principal  fusion  takes  place, 
is  provided  by  the  carbon 
crucible  D,  which  also  con- 
stitutes the  negative  elec- 
trode, being  provided  with 
suitable  means  for  connexion  FIG.  29. 

to  the  external  circuit. 

The  positive  electrode  E  also  consists  of  a  carbon  block, 
situated  in  the  upper  portion  of  the  structure,  just  above 
the  mouth  of  the  ore  inlet  A.  In  the  upper  wall  of  this 
latter  is  arranged  a  flue  F,  through  which  the  hot  gases 
evolved  during  the  process  make  their  escape,  and  pass 
over  into  the  preparatory  furnace,  where  they  are  utilized 
in  maintaining  the  necessary  heat.  H  is  an  intermediate,  or, 
as  the  inventor  terms  it,  "  false  "  electrode,  also  of  carbon. 

The  course  of  the  current  is  from  the  upper  electrode  E, 
across  the  ore  feed  inlet  to  H,  and  thence  through  the 
column  of  mixed  coke  and  ore  to  D. 

123 


ELECTRIC   FURNACES    AND 


A  primary  heat  zone  is  thus  created  at  the  point  of  entry 
of  the  ore,  where  it  is  most  needed,  and  the  process  is  con- 
tinued through  the  mixed  column  as  it  passes  down  to  the 
crucible  D,  where  the  molten  metal  is  collected,  and  drawn 
off  at  the  tap-hole  t ;  s  is  a  similar  tap-hole,  at  a  higher 
elevation,  for  the  removal  of  the  slag. 

Marcus  Ruthenberg  has  confined  his  attention  mainly 
to  the  design  and  perfecting  of  furnaces  and  processes  for 
the  treatment  of  such  ores  as,  by  virtue  of  their  finely 
divided  state,  offer  special  difficulties  in  the  way  of  treat- 
ment and  reduction  by  ordinary  smelting  furnace  methods. 
Such  ores  are,  not  infrequently,  exceedingly  rich  in  metal ; 
any  process,  therefore,  tending  towards  their  successful 
commercial  reduction,  should  be  welcomed  by  metallurgists 
and  the  mining  world  generally. 

An  ingenious  furnace  for  agglomerating  magnetic  sand, 

an  ore  extremely  rich  in 
pure  iron,  is  represented  in 
Fig.  30.  It  takes  the  form 
of  twin  cast-iron  hoppers, 
H  H,  hinged  together  at 
the  top,  as  shown,  by  an 
insulating  joint,  and  pro- 
vided with  a  ring  R  for 
suspension  from  a  suit- 
able support.  These  hop- 
pers converge  at  the  bot- 
tom to  opposing  discharge 
orifices,  d  d,  which  are 
water- jacketed  as  shown, 
for  the  purpose  of  keep- 
ing them  cool,  and  thereby 
preserving  them  from  de- 
struction by  the  great 
heat  evolved. 

FIG.  30.  Terminal  connexion  with 

124 


THEIR   INDUSTRIAL   APPLICATIONS 

the  hoppers  is  made  at  points  near  these  discharge  open- 
ings, and  a  screwed  rod,  and  hand  wheel  adjustment  W, 
about  half-way  up,  serves  to  regulate  the  distance  between 
them  at  the  will  of  the  operator. 

M  M  are  electro-magnet  windings  encircling  the  upper 
portion  of  the  hoppers,  and  energized  by  a  current  when 
the  furnace  is  working.  Both  hoppers  are  thus  rendered 
magnetically  active,  and  communicate  their  magnetism 
to  the  particles  of  magnetic  ore,  or  sand,  which  they  con- 
tain. Under  the  magnetic  influence,  these  particles  adhere 
together,  and,  as  they  emerge  from  the  discharge  orifices 
below,  agglomerate  into  masses,  which  are  then  subjected 
to  the  heating  effect  of  the  main  current  passing  through 
them  from  hopper  to  hopper,  the  latter  acting  as  terminal 
electrodes. 

The  agglomeration  is  thus  rendered  permanent,  and  the 
ore  falls  away,  in  plastic  masses,  into  the  crucible  C  placed 
below  to  receive  it.  In  this  form  it  is  more  readily  treated 
by  ordinary  smelting  processes. 

Another  patent,  granted  to  the  same  inventor,  for 
agglomerating  magnetite,  is  equally  ingenious  in  its  design 
and  construction.  It  consists  of  a  cast-iron  hopper  situated 
above,  and  discharging  immediately  on  to  the  periphery 
of  a  cast-iron  cylinder  below.  The  cylinder  and  hopper 
form  the  electrodes  of  the  main  furnace  circuit,  and  the 
former,  driven  by  a  motor,  through  a  worm  gear,  auto- 
matically draws  the  issuing  magnetite  away  from  the  dis- 
charge orifice  of  the  hopper,  whilst  at  the  same  time  it  is 
agglomerated,  as  in  the  previous  process,  by  the  heating 
effect  of  the  current.  The  discharge  orifice  of  the  hopper 
is,  of  course,  protected,  as  in  the  previous  furnace,  by  a 
cooling  water-jacket. 

If  so  desired  carbon  and  the  necessary  flux  ingredients 
may  be  introduced  to  form  a  mixture  with  the  crude  mag- 
netite before  subjecting  it  to  the  action  of  the  furnace,  and 
the  ore  thus  reduced  to  metal  in  a  single  operation. 

125 


ELECTRIC   FURNACES   AND 

The  Ruthenberg  process,  which  was  demonstrated  before 
a  committee  of  experts  in  January,  1903,  at  the  works  of 
the  Cowles  Electric  Smelting  Co.,  West  Lockport,  N.Y., 
consists,  briefly,  in  first  purifying  the  raw  ore  to  the  highest 
possible  degree,  incorporating  it  with  powdered  reducing 
material  in  the  shape  of  charcoal,  or  coke  dust,  and 
then  subjecting  it  to  the  action  of  one  of  the  furnaces  de- 
scribed above,  from  which  it  emerges  as  a  reduced,  fritted 
mass,  suitable  for  direct  use  in  steel  manufacture  without 
any  further  treatment. 

Some  33  per  cent,  of  fuel,  and  all  the  limestone  incidental 
to  the  ordinary  blast  furnace  process  is  thus  saved,  whilst 
the  resultant  steel  is  stated  to  be  of  a  better  and  purer 
quality  than  that  produced  by  ordinary  combustion  methods 
pure  and  simple. 

The  process  entails  the  combustion  of  500  kgs.  of  soft 
coal  per  ton  of  product,  of  which  150  kgs.  are  necessary  to 
effect  the  reduction.  The  expenditure  of  energy  necessary 
in  other  processes  to  maintain  the  fusion  of  the  entire  mass 
is,  in  the  Ruthenberg  process,  dispensed  with,  only  a  small 
portion  of  the  ore,  that  bridging  the  actual  terminals,  and 
constituting  the  resistance  core,  being  treated  at  a  time. 

The  terminals  of  the  electro-magnetic  arrangement  are 
identical  with  those  of  the  furnace  proper,  there  being  no 
electrodes,  in  the  ordinary  acceptation  of  the  term,  though 
the  water-cooled  discharge  openings  of  the  hoppers  really 
act  in  this  capacity. 

Prior  to  its  introduction  into  the  furnace  hoppers  the 
ore  is  purified  as  far  as  possible,  all  earthy  and  cinder- 
forming  matter  being  eliminated.  It  is  then  crushed,  the 
degree  of  granulation,  or  comminution,  being  largely  deter- 
mined by  the  quality  of  the  ore  ;  low  grade  ores  require 
to  be  finer  than  those  rich  in  metal.  The  crushed  ore  is 
then  mixed  with  the  necessary  ingredients,  and  in  the 
proportion  indicated  by  the  desired  analysis  of  the  product, 
and  introduced  into  the  hoppers.  The  high  temperature 

126 


THEIR   INDUSTRIAL   APPLICATIONS 

attained  at  the  discharge  orifices  fuses  it  into  a  homo- 
geneous mass,  denuded  of  a  portion  of  its  oxygen.  The 
remaining  complement  of  oxygen  is  eliminated  in  course 
of  cementation,  which  is  secured  by  keeping  the  mass 
heated  after  its  discharge  from  the  electric  furnace.  The 
final  treatment  or  fusion  is  effected  in  an  ordinary  open 
hearth  furnace. 

Ruthenberg  states  that  the  energy  required  in  smelting 
one  ton  of  iron  ore  by  his  process  is  500  k.w.  hours.  He 
further  claims  that  his  process  of  electrical  steel  manu- 
facture reduces  the  cost  20  per  cent.,  and  that  the  product 
is  superior  to  that  manufactured  by  the  Bessemer  process. 

He  has,  in  addition  to  the  apparatus  already  described, 
also  patented  another  resistance  furnace  process  for  the 
smelting  and  reduction  of  iron  ores  ;  the  process  consists 
essentially  in  thoroughly  incorporating  a  carbonaceous 
reducing  material  with  the  broken  fragments  of  ore,  coking 
it  in  place,  and  reducing  the  resultant  mass  to  spongy  iron, 
which  is  finally  fused. 

The  resistance  furnace  in  which  these  several  phases  of 
the  complete  process  are  effected  has  horizontal  electrodes, 
which  pass  through  the  walls  in  the  neighbourhood  of  the 
hearth,  the  heating  resistance  circuit  being  completed  by 
a  mass  of  the  molten  metal.  Immediately  above  this  is 
the  fusion  zone,  in  which  is  effected  the  fusion  of  the  spongy 
metal,  which  has  already  been  reduced,  at  a  still  higher 
level,  in  the  reduction  zone.  The  coking  zone  is  above 
this  latter  again,  and  the  process  is  effected  by  the  heat 
from  the  waste  gases,  which  play  over  the  mass  immediately 
after  it  has  been  charged  into  the  furnace. 

It  is  rumoured  that  a  number  of  Canadian  capitalists 
have  purchased  the  patent  rights  of  the  Ruthenberg  pro- 
cess of  electric  smelting  and  steel  production,  which  lends 
itself  readily  to  the  treatment  of  iron,  sand,  and  magnetic 
iron  ores.  They  will  construct  a  plant  on  the  Welland 
River,  at  Chippewa,  utilizing  Niagara  power  from  the 

127 


ELECTRIC  FURNACES   AND 

Canadian  side.  Their  object  is  to  work  the  extensive 
deposits  of  magnetic  ore  in  Ontario  and  Quebec,  in  the 
vicinity  of  which  fuel  is  scarce,  but  water-power  plentiful, 
a  double  recommendation  for  the  installation  of  an  electric 
furnace  plant.  The  outcome  of  this  industrial  venture 
will  be  awaited  with  interest. 

The  development  of  the  process  by  its  inventor  has  been 
of  an  encouraging  nature.  In  a  paper  before  the  American 
Electro-Chemical  Society  in  1902,  he  quoted  the  work  per- 
formed upon  one  ton  of  ore  by  the  electric  furnace  as  in 
the  neighbourhood  of  500  k.w.  hours.  In  a  subsequent 
paper  (1903)  the  inventor  was  able  to  announce  that  he 
had  brought  the  consumption  of  electrical  energy,  for  a 
similar  quantity  of  ore,  down  to  one-half  the  original  figure, 
or  250  k.w.  hours. 

The  Conley  furnace,  so  named  after  its  inventor,  Michael 
R.  Conley,  and  exploited  by  the  Conley  Electric  Furnace 
Company,  is  of  a  simple  design,  which  lends  itself  to  a 
variety  of  operations. 

The  furnace,  Fig.  31,  is  cylindrical,  being  constructed, 
as  usual,  of  fire-brick  F.  The  upper  portion  is  funnel- 
shaped,  as  shown,  and  constitutes  a  feed  hopper,  the  walls 
of  which  converge  to  a  contracted  portion  or  neck,  n, 
about  two-thirds  down,  where  the  primary  heat  zone  is 
situated.  Below  this  contraction  the  furnace  expands 
into  a  hearth  H  provided  with  a  tapping  hole  t,  where 
the  molten  furnace  products  collect,  and  are  drawn  off. 
Midway  between  the  contraction  and  the  floor  of  the  hearth 
is  placed  a  second  heat  zone,  n2,  which  either  per  se,  or  in 
combination  with  the  primary  zone,  n,  permits  a  variety 
of  combinations  in  the  way  of  electrical  connexion  of  the 
mains  carrying  the  current. 

The  furnace  is  of  the  resistance  type,  the  incandescent 
portion  consisting  partly  of  the  electrodes  e  e  and,  within 
the  furnace,  of  the  charge  itself.  The  electrodes  e  e  are 
segmental  in  form,  and  consist  of  a  graphite  clay  mixture  ; 

128 


THEIR    INDUSTRIAL   APPLICATIONS 


they  are  mounted  between  segmental  pillars  of  the  fire* 
brick  structure,  in  such  manner  as  to  permit  of  consider- 
able adjustment  to  compensate  for 
combustion  and  wear.  They  meet 
at  the  point  of  entry  into  the  fur- 
nace chamber,  and  form  a  contin- 
uous band,  which,  in  conjunction 
with  the  conducting  charge,  be- 
comes incandescent  when  the  re- 
quired current  is  passed  through. 
Each  segmental  electrode  is  pro- 
vided with  a  terminal,  and  it  will 
be  seen  that,  by  varying  the  elec- 
trical connexions  to  the  furnace, 
as  stated  above,  the  direction  of 
maximum  heat  can  be  varied  at 
will,  in  either  a  horizontal  or  ver- 
tical direction. 

As  already  mentioned,  the  furnace 
is  designed  for  a  number  of  uses, 
chief  among  which  are  the  reduc- 
tion of  iron  ores  and  the  manu- 
facture of  steel. 

In  Conley's  latest  form  of  resist- 
ance furnace  for  the  smelting  of  iron 
ores,  and  the  manufacture  of  steel, 

with  facilities  for  direct  casting  from  the  furnace  itself,  certain 
modifications  have  been  made  in  the  original  design,  de- 
scribed above.  It  consists,  as  before,  of  a  fire-brick  struc- 
ture, the  upper  portion  of  which  is  funnel-shaped,  and  has 
a  central  rib,  or  partition,  also  of  fire-brick.  The  walls 
of  the  funnel  converge  to  a  neck,  where  the  principal  heat 
zone  is  located.  Three  resistance  plates,  consisting  of 
one  part  graphite  to  three  of  fire-clay,  are  introduced  at 
this  point,  and  provided  with  terminals  for  connexion  to 
the  external  circuit.  The  section  of  the  central  portion 

129  K 


FIG.  31. 


ELECTRIC   FURNACES   AND 

of  these  plates  is  reduced,  in  order  to  increase  the  resist- 
ance, and,  consequently,  the  heating  effect.  Below  this 
heat  zone  the  furnace  expands,  as  before,  into  a  hearth  of 
larger  diameter,  where  the  molten  metal  collects  and  is 
maintained  in  a  fused  state  by  a  carbon  resistance  belt, 
also  provided  with  external  terminals,  as  in  the  previous 
design. 

An  especial  feature  of  the  furnace  consists  in  a  magnesite 
lining,  which  is  applied  to  all  exposed  carbon  surfaces  of 
the  resistances,  and  prevents  direct  contact  between  them 
and  the  charge  of  ore  to  be  reduced ;  the  carbon  required 
for  the  reaction  can  thus  be  exactly  computed,  and  the 
necessary  percentage  added  to  the  ore  without  fear  of 
subsequent  contamination  by  carbon  particles  which  might 
otherwise  become  detached  from  the  electrodes  themselves. 

Conley's  estimate  of  the  cost  of  steel  production  by  his 
process  runs  as  follows  :  Working  on  ores,  and  producing 
at  the  rate  of  100  tons  per  day  : — 

£ 
Electrical  energy  .          .          .          .          .          .          .50 

Thirty  tons  of  coke  at  8s.     .          .          .          .          .        12 

Two  hundred  tons  of  ore  (65  per  cent,  metal)  at  14s.  .      140 
Repairs  and  maintenance       .          .          .    '  10 

Labour          ,~         .-.        .          .          .          .         v         .       25 

Total       .          .          .          ;         ...   £237 
or  an  average  cost  of  £2  7s.  5d.  per  ton. 

Working  on  pig  iron  and  scrap,  and  producing  at  the 

rate  of  24  tons  per  day — 

£     s.    d. 
Electrical  energy  .          .          .          .  12  10     0 


Twelve  tons  of  wrought  iron  at  112s. 

,,  ,,  cast  iron  scrap  at  64s. 

Repairs  and  maintenance 
Labour  .       ''  . 


67     4     0 
38     8     0 
500 
13     0     0 


Total       .         '„          .      ;    .  £136     2     0 

or  an  average  cost  of  £5  13s.  Qd.  per  ton. 

Contardo's  furnace  for  the  reduction  of  metals  such  as 

130 


THEIR   INDUSTRIAL   APPLICATIONS 


iron  from  their  ores  and  the  manufacture  of  steel,  consists 
(Fig.  32)  of  three  distinct  parts,  or  chambers :  (A)  a 
funnel,  or  feed  hopper,  with  suitable  regulating  device,  and 
gas  outlet,  for  the  introduction  and  control  of  the  charge 
of  raw  material  or  ore  to  be  reduced.  (B)  an  intermediate 
portion,  or  hearth,  which  is  the  seat  of  the  necessary  heat, 
provided  by  an  arc  or  arcs, 
struck  between  diametrically 
opposed  electrodes  E,  and 
shielded  from  direct  contact 
with  the  charge  by  an  inverted 
V-shaped  roof  R  of  refractory 
material,  thus  protecting  the 
charge  from  the  introduction  of 
impurities,  such  as  might  be- 
come detached  from  the  elec- 
trodes themselves ;  and  (C),  a 
receiving  chamber,  or  crucible, 
for  the  reception  of  the  molten 
metal,  provided  with  the  usual 
tapping  hole  at  its  lowest  point, 
and  within  the  walls  of  which, 
communicating  with  suitable 
inlets,  are  passages,  or  flues  F 
for  the  introduction  of  reducing 
and  carburetting  gases,  respec- 
tively, into  the  presence  of  the 
heated  mass.  The  nature  of 
the  gases  introduced  through 

these  flues  is  determined  by  the  required  composition  of 
the  finished  product,  and  may,  if  the  process  be  one  of 
smelting  pure  and  simple,  be  either  omitted  altogether, 
or  regulated  as  desired. 

The  Stassano  process  for  the  electrical  production  of 
iron  and  steel,  consists,  briefly,  in  first  subjecting  the  ore 
to  a  process  from  which  it  emerges  in  a  state  of  fine  sub- 


FIG.  32. 


ELECTRIC    FURNACES    AND 

division.  Lime  and  coke,  also  ground  to  a  fine  powder, 
are  then  mixed  with  it  in  the  necessary  proportions,  and 
the  mixture,  aided  by  a  suitable  binding  material,  is  moulded 
into  briquettes,  in  which  form  it  is  subjected  to  heat  in 
specially  designed  arc  furnaces. 

The  process  is  continuous,  the  resultant  metal  and  slag 
being  tapped  off  at  regular  intervals.  An  experimental 
plant  was  installed  at  Cerchi,  in  Italy,  the  furnace  being 
three  metres  high,  and  calling  for  an  expenditure  of  1,800 
amperes  at  50  volts  for  an  output  of  30  kgs.  of  metal  per  hour. 

In  the  original  experiments  with  the  Stassano  process 
of  iron  and  steel  production,  1  kg.  of  manganiferous  steel 
involved  an  expenditure  of  4'08  E.H.P.  hours  ;  this  figure, 
has,  however,  since  been  reduced  to  2*7  E.H.P.  hours  for 
an  equivalent  output. 

The  process  consists,  in  the  main,  in  substituting  an 
arc  furnace  for  the  blast  furnace  at  present  employed,  and 
feeding  the  material  to  be  treated,  into  it,  in  the  form  of 
briquettes,  consisting  of  iron  ore  and  carbon,  lime,  and 
tar,  as  a  binding  material.  The  process  is  synonymous 
with  that  which  takes  place  in  a  blast  furnace,  the  ores 
being  reduced  by  the  carbon  and  the  siliceous  remainder 
removed  in  the  form  of  slag. 

The  ores  most  usually  treated  are  those  in  which  the 
metal  exists  as  a  carbonate  or  oxide  ;  if  the  former,  the  ore 
requires  to  be  initially  roasted.  Previous  to  subjecting 
them  to  the  action  of  the  arc,  all  ores  are  powdered  and 
mixed  with  the  proportions  of  carbon,  lime,  and  silica, 
which  a  prior  analysis  of  the  ore  may  show  to  be  necessary. 
From  5  to  10  per  cent,  of  pitch  is  then  added  as  a  binding 
material,  and  the  mass  moulded  into  briquettes  by  hydraulic 
pressure. 

About  half  an  hour  is  the  time  required  in  producing  suffi- 
cient metal  to  form  a  small  ingot,  the  power  consumption 
being  in  the  neighbourhood  of  3,000  H.P.  for  each  ton  of 
metal  produced. 

132 


THEIR    INDUSTRIAL    APPLICATIONS 

The  Stassano  electric  smelting  works  are  in  operation  at 
Darfo,  near  the  Lago  d'Isco.  According  to  Goldschmidt, 
Stassano  has  succeeded  in  producing  soft  iron,  with  a  carbon 
content  less  than  0'2  per  cent.,  directly  from  iron  ore  on  a 
commercial  scale  in  the  electric  furnace.  It  is  necessary  to 
add  that  very  pure  ores  are  available,  as  the  following  table 
of  chemical  compositions  will  show — 

CHEMICAL   COMPOSITION   OF   ITALIAN   ORES. 

SUBSTANCE.      MAGNETITE.       KED  HAEMATITE.  LIMONITE.  LIMONITE. 
Fc3O4  .            78-400% 

88-850%  80-930%  73-840% 

0-470%  0-567%  0-567% 


Fe0O 


2^3 


MnO 

8i02 

AlaO: 

CaO 

MgO 

S    . 

P   . 


8-650%  2-960%  1-970%  1-970% 

7-330%  3-420%  2-152%  2-152% 

0-870%  0-590%  0-590% 


1-030% 


0-078%  0-070%  0-070% 

0-093%  0-124%  0-124% 


A  consideration  of  the  energy  required,  and  cost,  of  the 
electrical  process  devised  by  Stassano,  yields  the  following 
figures.  Working  at  an  efficiency  of  80  per  cent.,  1  H.P.  hour 
is  equivalent  to  508' 2  Calories,  or  the  heat  derived  from 
1  kilogramme  of  coal  is  equal  to  3  H.P.  hours.  Cost  of  insta- 
lation,  per  E.H.P.,  £12 ;  annual  cost  (10 per  cent,  for  interest 
and  depreciation,  £1  4s.,  maintenance,  8s.)  £1  12s.  The  cost 
of  1  H.P.  hour,  on  the  basis  of  7,000  working  hours  per 
annum,  is  therefore  0'055d. 

In  the  Stassano  furnace,  the  charge  is  heated  solely  by 
radiation,  the  heat  of  the  arc,  which  is  maintained  by  2,000 
amperes  at  170  volts,  alternating  current,  being  reflected  on 
to  the  charge  by  a  domed  roof. 

The  electrodes  pass  through  water-cooled  sleeves,  and  are 
supported  by  conducting  rods,  sliding  in  gas-tight  glands, 
and  adjustable  therein,  by  means  of  small  hydraulic  cylin- 
ders, which  afford  a  simple  and  convenient  means  of  feeding 
or  withdrawing  the  carbons.  Once  the  action  is  started,  the 
arc  is  drawn  out  to  as  great  a  length  as  one  metre,  the  oper- 

133 


ELECTRIC    FURNACES    AND 

ation  of   the   furnace   being  accompanied  by   considerable 
noise. 

A  great  measure  of  the  success  attained  by  Captain  Stas- 
sano  in  his  electric  smelting  process  is  attributed  by  Gold- 
schmidt  to  the  care  bestowed  upon  the  composition  of  the 
furnace  charge,  with  a  view  to  securing  complete  reduction 
and  a  maximum  yield.  The  following  table  represents  the 
percentage  composition  of  a  typical  Stassano  furnace  charge, 
which,  thoroughly  incorporated,  and  mixed  with  tar  as  a 
binding  material,  is  moulded  into  briquettes  prior  to  its  in- 
troduction into  the  furnace. 

ORES.  FLUXES.  COAL.  TAR. 

Fe2O3      93-02%  CaO  .      51-21%  C       .   90-42%     C.      .      59-2% 

MnO  .       0-610%  MgO.        3-11%  Ash   .      3-88%     Hydro- 
carbons 40-5% 

Si02     .     3-79%  A1203\    0-0/     H20   .     5-70%     Ash      .     0-27% 

S    .      .      0-058%  Fe2O3J  /0 

P  .      .      0-056%  SiO2     .    0-9% 

0-5%  C02  ._43.43% 

H20    .      1-72% 

A  charge  consists  of  ores,  100  kgs.  ;  coal,  23  kgs.  ;  and 
fluxes,  12' 5  kgs.,  the  various  constituents  being  apportioned 
as  follows — 

ORES.  COAL.  FLUXES. 


Fe203 

.    93-02  kgs. 

C      . 

20-9  kgs. 

CaO      . 

6-401  kgs. 

MnO. 

.     0-619  ~, 

Ash  . 

0-892    „ 

MgO     . 

0-389    „ 

Si02. 

s 

.     3-79     „ 
.      0-058  „ 

H20. 

1-21      „ 

A1203) 
Fe20j 

0-062    „ 

P     . 

.      0-056  „ 

Si02      . 

1-125    „ 

CaO    \ 
MgO  J 

0-5       „ 

C02       . 

5-429    „ 

H20 

.      1-72    „ 

— 

— 

The  resultant  metal  has  the  following  composition- 


Iron 

Manganese 
Silicon 
Sulphur     . 
Phosphorus 
Carbon 


99-764  percent. 
0-092     „ 
Trace. 

0-059     „        „ 
0-009     „ 
0-090 


134 


THEIR    INDUSTRIAL    APPLICATIONS 


The  following  thermal  data  regarding  the  heat  required 
for  bringing  about  the  various  stages  of  the  process  are 
quoted — 


For  the  reduction  of  1  gramme-molecule  of 
Fe203  .  .  .  . 

For  the  conversion  of  1  kg.  of  water  at  100°C. 
=  212°F.  into  steam,  at  the  same  tem- 
perature ...... 

For  raising  the  temperature  of  1  kg.  of  steam 
at  1000C.,  by  1°C 

For  calcining  1  kg.  of  flux 

For  raising  the  temperature  of  1  gramme- 
molecule  of  CO2,  1°C.  .  . 

For  raising  the  temperature  of  1  gramme- 
molecule  of  CO,  1°C. 

For  fusing  1.  kg.  of  iron    .... 

For  fusing  1  kg.  of  slag    .... 

The  combustion  of  1  kg.  of  C  to  CO,  generates 

Required,  for  the  decomposition  of  ferric 
92-02x192 


oxide 


0-16 


For  the  evaporation  of  the  water  contained  in 
the  ore  and  coal  (1-72  + 1-21)  637  . 

Required,  to  superheat  the  steam  to  500°C. 
=  932°F.,  2-93  x  0-048  x  400 

Required,  for  calcining  the  flux  12-5  x425     . 

Required,  for  raising  the  temperature  of  the 
C02  toSOO'C.  51429  x  0-016x500 


0-044 
the    CO 


generated, 


Required,  for    heating 

On.Q 

0^12  x  0-0068x500=        . 

Required,     for     fusing    the    iron    produced, 

65  x  350      .          .          .          .          . 
Required,  for  fusing  the  slag,  13-89  x600     . 

Total  . 

The  oxidation  of  C,  to  CO,  produces  20-9  x 
2,175= 

Balance 


CALORIES. 
192-000 

637-000 

0-480 
425-000 

0-016 

0-0068 
350-000 
600-000 
2,175-000 

111,552-000 

1,866-41 

562-56 
5,312-5 

987-09 
5,921-667 


22,775-2 
8,334-0 

157,311-427 


45,457-500 
111,853-927 


Assuming,  therefore,  an  efficiency  of  80  per  cent.,  this 
total  of 

135 


ELECTRIC   FURNACES    AND 


111,853-927  Calories,  =  =  219'08  H.P.  hours, 

635-3x0-80 

or,  the  yield  being  65'114  kilogrammes  of  iron,  the  energy 
required  for  the  production  of  1  kg.  is 

219-080  =  3.364       p    h 

65-114 

and  the  cost,  based  on  the  foregoing  estimate  of  0'055d£.  per 
H.P.  hour,  works  out  at  155.  5d.  per  ton. 

A  smaller  model  of  the  Stassano  furnace,  which  is  used 
for  experimental  purposes  at  Darfo,  requires  1,000  amperes 
at  80  volts. 

Turin  is  at  present  the  scene  of  Stassano'  s  electric  smelt- 
ing operations,  where  he  is  conducting  experiments  with  his 
process,  on  behalf  of  the  Italian  Government. 

Assuming  a  plant  of  5,000  H.P.,  producing  steel  at  the  rate 
of  30  tons  per  day,  with  a  thermal  efficiency  of  about  66  per 
cent.,  Stassano  estimates  the  cost  of  manufacturing  1,000 

kgs.  to  be  as  follows  — 

£  s.     d. 

1,600  kgs.  of  ore  at  12s.  per  ton      .          .          .      0  19     2£ 

For  pulverization  of  same  at  2s.  5d.  per  ton.      0  3  10 

200  kgs.  of  flux  at  4s.  per  ton  .          .      0  0  10 


250  kgs.  of  coke  at  36s.  per  ton 

Crushing  same  at  Is.  7d.  per  ton 

190  kgs.  of  other  materials  (tar,  etc.)  at    56s 

per  ton 

Mixing  at  2s.   5d.  per  ton 
Wear  of  electrodes,   12  kgs. 
Labour 
Maintenance  of  furnace 


090 
005 

0  10  8 
055 
0  2  lO 
0  4  9 
097 
025 


Accessories 

Electrical  energy,  4,000  H.P.  hours  at  0-0o5d. .  0  18     3 

Other  costs  .          0.      .          .          .          .  0     2     4 

Total  498 


Less  the  value  of  inflammable  gases,  900  cubic 

metres  at  0-1 92d.  .          .          .          .      0  14     5 


Nett  Cost  .          .          .          .    £3  15     3 

Dr.  Goldschmidt,  in  a  paper  before  the  Electro-Chemical 

136 


THEIR    INDUSTRIAL    APPLICATIONS 

Society  of  Cologne  (1903),  gave  some  interesting  particulars 
regarding  the  Stassano  process.  The  following  are  a  few  of 
the  salient  points  mentioned. 

The  current  used  in  the  experiments  which  have  been 
carried  out  at  Darfo,  in  Italy,  is  alternating,  and  is  derived 
from  two  large  dynamos,  each  of  500  H.P.,  and  a  smaller  one 
of  100  H.P.  The  process,  like  other  reduction  methods,  con- 
sists essentially  in  reducing  the  iron  ores  with  charcoal  or 
coke,  by  virtue  of  the  heat  derived  from  an  electric  arc,  work- 
ing above  the  charge,  suitable  fluxes  being  introduced,  to 
eliminate  undesirable  impurities. 

The  latest  form  of  Stassano  furnace  consists  of  a  closed 
cylindrical  structure,  with  domed  roof,  constructed  of 
masonry,  and  having  a  cavity  one  metre  in  diameter  and 
one  metre  high.  A  sloping  feed  channel  serves  for  the  intro- 
duction of  the  ore,  whilst  two  tapping  holes,  at  different 
elevations,  provide  for  the  withdrawal  of  the  molten  metal 
and  slag  respectively.  The  entire  furnace  can  be  revolved 
around  a  vertical  axis. 

The  electrodes  are  introduced  through  the  walls  at  oppo- 
site extremities  of  a  diameter,  and  at  or  about  the  centre  of 
the  furnace  cavity;  at  the  commencement  of  the  process 
their  inner  extremities  are  close  together,  but,  as  the  opera- 
tion proceeds  and  the  temperature  increases,  they  are  with- 
drawn until  the  arc  extends  across  the  entire  width  of  the 
furnace  cavity. 

With  the  arc  at  its  maximum,  the  current  is  so  regulated 
that  in — 

20  minutes,  the  E.M.F.  is  80  volts,  and  the  current  800  amperes. 
40  „  „  „  100  „  „  „  1,000 

70       „         „         „  70     „  „  „  600 

100       „         „         „  50     „  „  „  500 

The  entire  reduction  process  occupies  two  hours,  from 
first  switching  on,  until  the  reduced  metal  is  ready  for  cast- 
ing, during  the  first  half  of  which  period  the  charge  is  being 
introduced. 

137 


ELECTRIC    FURNACES    AND 

The  following  is  the  composition  of  a  typical  charge,  which 
was  reduced  by  a  current  of  1,000  amperes  at  80  volts- 
Iron  ore    .          . 1,000  parts. 

Limestone  .          .          .          .          .          .         125      „ 

Carbon      .  .  .          .          .  .  .         160      „ 

Miscellaneous  (hydrocarbons,  etc.)        .          .         120      „ 

The  total  weight  of  the  above  charge  was  70' 25  kgs.,  and 
the  following  table  represents  the  original  weight  of  redu- 
cible substances,  together  with  the  weights  actually  obtained 
in  the  process — 

SUBSTANCE.  ORIGINAL  WEIGHT  (GRAMMES).  PRODUCT  (GRAMMES). 
Iron                                          32,557  30,727 

Manganese  239-7  28-3 

Silicon  910  Traces 

Sulphur  29  15 

Phosphorus  28  2-7 

The  actual  yield  was  thus  30'8  kgs.  of  wrought  iron. 

Below  will  be  found  a  tabular  analysis  of  the  impurities 
in  four  different  samples  of  steel  manufactured  by  the  Stas- 
sano  process. 

I.  II.                        III.               IV.  (CHROME 

STEEL). 

Carbon    .      .      0-04%  0-09%                  0-17%                  1-51% 

Manganese  .      0-05%  0-18%                  0-17%                  0-26% 

Silicon           .  Trace                  Trace 

Sulphur        .  0-05% 

Phosphorus  0-029% 

Chromium    .  1-22% 

An  iron  and  steel  plant,  at  Gysinge,  Sweden,  employing 
electric  furnaces  designed  by  M.  F.  A.  Kjellin,  is  now  produc- 
ing steel  of  excellent  quality,  which  is  unusually  dense  and 
homogeneous.  It  is  very  tough,  and,  when  annealed,  can 
be  readily  worked  in  a  cold  state,  without  any  tendency  to 
distortion  consequent  on  hardening,  as  is  frequently  the  case 
with  ordinary  grades  of  steel. 

The  inventor  attributes  the  improved  quality  of  the  steel, 
manufactured  by  his  process,  to  the  almost  complete  absence 
of  gaseous  matter,  especially  hydrogen. 

138 


THEIR    INDUSTRIAL    APPLICATIONS 

The  capacity  of  the  latest  Kjellin  furnace,  installed  at 
Gysinge,  is  1,880  kgs.,  and,  charged  with  raw  materials  in  a 
cold  state,  it  is  capable  of  producing  1,500  tons  of  steel  per 
annum.  It  is  supplied  with  current  from  a  single-phase 
alternating  current  generator,  driven  by  a  vertical  turbine, 
capable  of  developing  300  H.P. 

The  principal  considerations  which  led  to  the  design  of 
the  Kjellin  furnace  are  as  follows.  M.  Kjellin  early  recog- 
nized the  fact  that  in  operating  steel  furnaces  on  the  ordinary 
resistance  principle,  with  independent  electrodes,  the  molten 
metal  absorbs  impurities  from  the  latter,  which,  especially 
if  of  carbon,  are  also  consumed,  and  thus  add  to  the  expense 
of  the  operation,  whilst  the  carbon  monoxide  gas  formed  as 
a  result  of  the  combustion,  hinders  the  elimination  of  this 
gas  from  the  mass  of  the  steel  itself.  On  the  other  hand,  if 
carbon  be  dispensed  with,  and  the  current  led  direct  to  the 
mass  of  metal  under  treatment,  the  enormous  currents  re- 
quired necessitate  the  use  of  copper  leading-in  cables  at 
least  equal,  in  cross-sectional  area,  to  the  resistance  column 
of  metal. 

Water-cooled  iron  terminals  have  been  suggested,  but 
fresh  difficulties  arise  out  of  the  magnetization  effects  ;  more- 
over, the  use  of  alternating  currents,  one  of  the  desirable 
incidentals  to  such  a  large  power  conversion,  leads  to  fresh 
complications,  owing  to  skin  effect,  hysteresis,  and  conse- 
quent loss  of  power. 

With  a  view  to  surmounting  these  various  difficulties, 
Kjellin,  in  1899,  suggested  to  M.  Benedicks,  general  manager 
of  the  works  at  Gysinge,  the  form  of  construction  now  known 
as  the  Kjellin  furnace.  It  consists  of  an  annular  groove,  or 
hearth,  built  of  refractory  bricks,  and  closed  in  at  the  top 
by  refractory  covers,  which  are  removable  for  charging 
purposes. 

Centrally,  within  this  ring  is  placed  one  limb  of  a  rectan- 
gular iron  core,  built  up  of  thin  sheet-iron  laminations,  upon 
which  is  wound  a  cojpper  wire  coil,  which  constitutes  the 

139 

OF 

UNIVERSITY 


f  UN 
^S£ 


ELECTRIC   FURNACES    AND 

primary  winding  of  a  closed-circuit,  step-down  transformer, 
the  secondary,  in  the  shape  of  the  contents  of  the  annular 
hearth,  having  only  one  turn.  Current  is  supplied  to  this 
primary  winding  at  a  pressure  of  3,000  volts,  and  the  ratio 
of  transformation  is  such  that  the  current  through  the 
furnace  charge  is  approximately  equal  to  the  primary  cur- 
rent multiplied  by  the  number  of  turns  in  the  primary 
winding,  or  about  30,000  amperes. 

The  first  Kjellin  furnace  was  installed  at  Gy singe  in  Feb- 
ruary, 1900,  and  the  first  ingot  of  steel  successfully  cast  on 
the  18th  of  the  following  month,  the  expenditure  of  energy 
being  78  kilowatts  for  24  hours,  and  the  yield  270  kgs.  An 
improved  efficiency  was  secured  in  November,  1900,  when  a 
second  furnace  was  completed,  capable  of  producing  from 
600  to  700  kgs.  of  steel  in  24  hours,  with  an  energy  expendi- 
ture of  58  k.w.  With  this  construction,  however,  the  avail- 
able cooling  surface,  and  consequent  radiation  losses  were 
out  of  all  proportion  to  the  furnace  capacity,  and,  in  1902, 
a  neighbouring  sulphite  pulp  mill  having  been  destroyed  by 
fire  a  year  previously,  its  available  water  power  was  adapted 
to  steel  manufacture  on  the  Kjellin  principle,  with  the  result 
that  a  third  furnace  was  constructed,  and  has  been  work- 
ing satisfactorily  since  May,  1902. 

It  has  a  capacity  of  1,800  kgs.  of  charge,  1,000  kgs.  of  steel 
being  tapped  off  at  a  time,  leaving  the  remaining  800  kgs.  to 
complete  the  secondary  circuit  and  avoid  shutting  down  the 
power  plant.  The  output  is  4,100  kgs.  of  steel  in  24  hours, 
with  an  energy  expenditure  of  165  k.w.,  or  225  E.H.P.,  the 
charge  being  introduced  into  the  furnace  in  a  cold  state. 

The  raw  materials  employed  are  Dannemore  pig  iron  and 
wrought  iron,  which  are  fed  into  the  furnace  along  with  scrap 
steel,  and  in  the  proportions  indicated  by  experience,  as 
yielding  the  best  percentage  of  carbon. 

M.  Kjellin  is  reported  to  have  spoken  as  follows  regarding 
his  invention — 

"  By  the  electric  furnace  described,  the  steel  has  no  op- 

140 


THEIR    INDUSTRIAL  APPLICATIONS 

portunity  of  taking  up  such  gases,  or  other  impurities,  and 
the  quality  is  also  better  than  that  of  crucible  steel  with  the 
same  analysis.  To  make  special  steels  with  nickel,  tungsten 
or  chromium,  offers  no  difficulties,  and  the  alloys  are  quite 
homogeneous.  The  cost  of  production  depends,  principally 
on  the  efficiency  of  the  furnace  and  the  price  of  power. 

"  At  the  furnace  now  in  use  at  Gysinge,  the  losses  have 
been  experimentally  proved  to  be  87*5  k.w.,  so  that  the 
effective  power  absorbed  by  the  steel  is  165  —87*5  =  77*5  k.w., 
and,  as  these  produced  4,100  kgs.  of  steel  in  24  hours,  one 
effective  kilowatt  produces  about  53  kgs.  of  steel  ingots  in 
the  same  time.  Every  kilowatt  more  in  the  furnace,  when 
the  size  is  not  altered,  increases,  then,  the  output  with  53  kg. 
steel  ingots,  and  we  calculate,  when,  within  a  few  months, 
we  get  a  stronger  water  wheel,  to  produce  about  6,000  kgs. 
of  steel  ingots  with  200  k.w.  in  24  hours. 

"  As  the  absolute  cost  of  labour  and  repair  will  be  the 
same,  these  costs  for  one  ton  of  steel  ingots  will  be  about  two- 
thirds  of  the  cost  now,  and  the  price  of  power,  per  ton,  will 
also  be  sensibly  diminished. 

"  Thus,  a  furnace  of  736  k.w.,  or  1,000  E.H.P.  will  produce 
30,000  kgs.  of  steel  ingots  in  24  hours  when  charged  with  cold 
materials.  With  hot  materials  the  output  is  much  greater. 
For  instance,  if  250  kgs.  of  molten  pig  iron  are  charged  for 
each  ton  of  steel  ingots  produced,  the  output  is  increased 
from  30,000  to  36,000  kgs.  in  24  hours  with  the  same  ex- 
penditure of  energy. 

"  The  cost  of  labour  and  repair  for  such  a  furnace  will, 
in  my  opinion,  be  less  that  those  of  an  open-hearth  furnace 
of  the  same  size,  so  that,  where  power  is  cheap,  there  is  a 
possibility  of  producing  a  steel  at  a  smelting  cost  not  ex- 
ceeding that  of  the  open-hearth  furnace." 

The  following  is  a  detailed  estimate  of  the  cost  of  the 
Kjellin  process,  based  on  data  obtained  in  actual  practice  at 
Gysinge — 

4,100  kgs.  of  steel  are  produced  in  24  hours,  with  an 

141 


ELECTRIC   FURNACES   AND 

energy  expenditure  of  225  x  24  H.P.  hours  ;   1,000  kgs.  re- 
quire, therefore,   1,320  H.P.  hours. 

£     *.    d. 
Cost  of  electrical  energy,  assuming  1  H.P.  hour 

to  cost  0-18d 100 

Charge  (pure  charcoal,  cast  iron  and  wrought  iron)     6  10     0 
Repairs  and  lining  .  .          .  .          .      0     9     3| 

Depreciation  and  interest         .  .  .          .023 

Labour  0  10     0 


Total  cost,  excepting  royalties,  business  charges, 

etc .   £8  11     6J 

In  the  Kjellin  process  the  furnace  gases  do  not  come  into 
contact  with  the  steel.  The  cost  of  the  furnace  is  given  as 
15,000  kronen  (£832). 

The  following  table  gives  the  analyses  of  three  samples 
of  steel  manufactured  by  the  Kjellin  process  at  Gy singe — 

I.  ii.                     in. 

Carbon  .           .            1-45%  1-20%  0-95% 

Silicon    .          .            0-47%  0-74%  0-35% 

Manganese       .            0-49%  0-46%  0-33% 

Phosphorus     .             0-011%  0-013%  0-014% 

Sulphur            .             0-010%  0-010%  0-015% 

Other  Metals. — One  of  the  difficulties  incidental  to  re- 
duction processes,  as  carried  out  in  the  electric  furnace,  is 
that  the  molten  metal  formed,  readily  absorbs  the  carbon 
of  which  the  electrodes  are  composed,  and  thereby  becomes 
contaminated. 

Several  inventors,  realizing  the  importance  of  this  draw- 
back to  electric  smelting,  have  set  themselves  the  task  of 
providing  a  remedy.  E.  G.  Acheson  has  patented  a  method 
of  protecting  the  carbon  core  in  resistance  furnaces  by  coat- 
ing it  with  a  refractory  sheath  of  a  carbide,  which,  whilst 
preventing  actual  contact  between  core  and  charge,  never- 
theless conducts  the  heat  generated  by  the  former  to  the 
mass  of  the  latter. 

M.  Simon,  whilst  investigating  the  possibilities  of  pre- 
paring metallic  manganese  in  the  electric  furnace,  also 
experienced  this  difficulty,  but  succeeded  in  overcoming  it  by 

142 


THEIR    INDUSTRIAL   APPLICATIONS 

enveloping  the  anode  in  a  sheath  of  manganese  slag,  in 
which  the  metal  existed  as  the  lower  oxide,  and  was  there- 
fore inactive  in  the  presence  of  carbon. 

George  Egly  protects  the  lower  electrode  or  cathode,  in 
his  furnace  for  the  reduction  of  protoxide  of  nickel,  by 
covering  it  with  a  layer  of  magnesia,  about  2  c.m.  in  thick- 
ness. 

In  1895,  Moissan  succeeded  in  producing  silicon  in  the 
electric  arc  furnace  by  reducing  silica,  in  the  form  of  quartz, 
with  carbon,  in  a  coke  crucible.  Acheson  has  since,  1902, 
applied  the  resistance  furnace  principle  to  this  process, 
utilizing  graphite  as  a  reducing  agent.  To  this  end,  he 
mixes  silica  and  graphite  in  the  proportions  necessary  to  the 
reaction,  and  forms  the  resultant  mixture  into  a  column 
or  pyramid,  which  he  utilizes  as  a  conducting  core  in  a 
resistance  furnace.  This  admixture  of  graphite  with  the 
silica,  imparts  sufficient  conductivity  to  the  mass  ;  thus, 
it  was  found  by  experiment  that  a  core  two  by  two,  by 
three  inches,  had  an  initial  resistance  of  33  ohms,  which 
fell  to  5  ohms  as  the  reduction  proceeded. 

The  success  of  the  above  and  similar  experiments  has 
led  Acheson  to  take  out  a  patent  covering  the  applications 
of  graphite  as  a  reducing  agent  for  use  in  electric  furnaces 
of  the  resistance  type.  The  essential  properties  which 
fit  it  for  use  as  such  are — 

(1)  Its   high   purity,   and   consequent   inability   to   con- 
taminate any  ores  heated  in  its  presence. 

(2)  High  electrical  and  thermal  conductivity,   whereby 
the  necessary  current  is  transmitted  and  the  resultant  heat 
evenly  distributed. 

(3)  Extreme  divisibility,  permitting  an  advanced  degree 
of  comminution,  thereby  lending  itself  to  the  production  of 
an  intimate  mixture  with  the  ore  to  be  reduced. 

The  Tone  furnace,  invented  by  Mr.  P.  J.  Tone,  engineer 
to  the  Carborundum  Company,  Niagara  Falls,  has  been 
devised  with  a  view  to  overcoming  one  of  the  drawbacks 

143 


ELECTRIC   FURNACES   AND 


incidental  to  electric  smelting,  where  carbon  is  used  as  a 
reducing  agent,  viz.,  the  tendency  on  the  part  of  the  liber- 
ated metal  to  recombine  with  the  excess  of  carbon  present 
in  the  furnace  charge,  to  form  a  carbide.  As  already  stated, 
this  has  been  a  common  experience  with  metallurgists  in 
treating  the  ore  of  a  metal  whose  temperatures  of  reduction 
and  volatilization  are  approximately  the  same. 

In  the  Tone  furnace,  illustrated  in  Fig.  33,  this  ten- 
dency is  overcome  by  a  more  general  distribution  of  the 

heat  generated  in  the  furnace, 
combined  with  a  judicious  dis- 
tribution of  the  charge  about 
the  central  source  of  that  heat. 
The  charge  C  is  thoroughly 
mixed,  and  so  arranged  about 
the  resistance  core  R  as  to 
permit  globules  of  the  reduced 
metal  to  form,  and  descend  by 
gravitation  to  the  lower  portion 
of  the  structure,  whence  they 
drip,  finally,  into  the  recept- 
acles A  A.  E  E  are  the  ter- 
minal electrodes,  arranged  at 
the  upper  and  lower  extremities 
of  the  core  B,  which  consists 
of  a  pyramidal  pile  of  carbon 
blocks,  with  intervening  spaces. 

The  temperature  of  the  furnace  needs  to  be  very  carefully 
regulated,  such  that  the  reduced  metal  is  not  volatilized, 
whilst  the  heating  effect  is  evenly  distributed  and  general 
throughout  the  mass. 

Copper. — The  Heroult  process  has  been  applied  to  the 
extraction  of  metallic  copper  from  its  ores.     In  1903,  ex- 
periments conducted  at  La  Praz,  France,  under  the  personal 
supervision  of  the  inventor,  yielded  satisfactory  results. 
In    connexion    with    these    experiments,    the     following 

144 


FIG.  33. 


THEIR   INDUSTRIAL   APPLICATIONS 


details  have  been  made  public.  Two  carbon  electrodes,  of 
square  cross-section,  were  used,  each  side  being  25  c.m. 
The  mineral,  which  contained  7  per  cent,  metallic  copper, 
was  placed  in  a  rectangular  crucible,  the  electrodes  de- 
scending vertically  into  it.  Eighteen  tons  of  ore  were 
treated  in  24  hours,  the  resultant  matte  containing  from 
43  to  45  per  cent,  copper,  whilst  the  slag  only  retained  from 
O'l  to  0*2  per  cent,  of  the  metal.  The  current  required  to 
effect  this  result  was  from  3,500  to  4,000  amperes  at  110 
volts. 

M.M.  Keller,  Leleux,  &  Co.  have  also  conducted  experi- 
ments on  the  electrical  extraction  of  metallic  copper  from 
its  ores,  utilizing  a  Keller  furnace  with  two  centres  of  ac- 
tivity, each  provided  with  an  independent  pair  of  electrodes. 
The  actual  reduction  is  effected  in  the  first  heat  zone,  the 
second  serving  to  maintain  the  high  temperature  of  the 
mass,  pending  the  thorough  separation  of  matte  and  slag. 

Twenty-five  tons  of  ore  were  treated  in  24  hours,  the 
power  consumed  being  500  k.w.  The  consumption  of 
electrodes  amounted  to  from  5  to  7  kgs.  per  ton  of  ore. 

The  composition  of  the  resultant  matte  was  as  follows — 

per  cent. 


Silica 

Aluminium 

Iron 

Manganese 

Sulphur 

Phosphorus 

Copper 

And  of  the  slag — 

Silica 

Alumina 

Lime 

Magnesia 

Iron 

Manganese 

Sulphur 

Phosphorus 

Copper 


0-8 

0-5 
24-3 

1-4 
22-96 

0-005 
47-9 


27-2 

5-2 

9-9 

0-39 
32-5 

8-23 

5-7 

0-062 

0-1 


per  cent. 


The  above  trials  were  carried  out  in  the  presence  of  M.  Ch. 

145  L 


ELECTRIC    FURNACES    AND 

Vattier,  who,  acting  under  a  commission  from  the  Chilian 
Government,  has  lately  visited  France  for  the  purpose  of 
carrying  out  experiments  in  the  electrical  smelting  of  copper 
ores. 

M.  Vattier's  report  contains  some  interesting  comparative 
figures  relating  to  costs,  etc.  In  the  coke  furnaces  at  present 
in  vogue  in  Chili,  3,200  kgs.  of  coke,  costing  £13,  are  required 
for  each  ton  of  copper  produced.  On  the  other  hand,  a 
consumption  of  1*25  k.w.  year,  is  estimated  as  sufficient 
to  smelt  16  tons  of  ore,  corresponding  to  one  ton  of  copper, 
in  the  electric  furnace.  Assuming  the  cost  of  1  k.w.  year  to 
be  24s.,  a  figure  based  on  the  abundance  of  water  power  in 
Chili,  the  cost  of  energy  per  ton  of  copper  produced  would 
amount  to  30s.,  and,  allowing  36s.  for  electrodes,  etc.,  the 
total  cost  of  production  per  ton  of  metal  works  out  at 
£3  6s. 

Arsenic. — The  importance  of  arsenic  as  a  marketable 
commodity  may  be  gauged  from  the  facts,  published  by  the 
Mineral  Industry,  that  the  total  output  for  1900  was  7,300 
metric  tons,  produced  by  Great  Britain,  Germany,  Italy, 
Spain,  and  Canada,  the  two  first  named  being  the  principal 
manufacturers.  The  demand  is  said  to  be  quite  equal 
to  the  supply,  so  that  there  is  little  doubt  as  to  the  need  for 
this  useful  metal. 

Unfortunately,  the  ordinary  metallurgical  processes  for 
its  extraction  from  the  various  arsenic  -  bearing  ores  possess 
many  attendant  disadvantages,  not  the  least  of  which 
arise  out  of  the  poisonous  nature  of  the  fumes  given  off 
during  the  process,  and  their  deleterious  effect  on  the 
surrounding  animal  and  vegetable  kingdom. 

This  is  all  the  more  unfortunate  in  that  many  of  the 
well-known  arsenic  bearing  ores  are  also  rich  in  gold  and 
other  noble  metals.  An  improved  process,  therefore, 
calculated  to  increase  the  output  and  efficiency  of  ex- 
traction, would  doubtless  be  welcomed  by  metallurgists 
in  general. 

146 


THEIR   INDUSTRIAL   APPLICATIONS 

Such  a  process,  applicable  to  at  least  one  rich  grade  of 
arsenic  ore,  has  been  invented  by  Mr.  G.  M.  Westman,  of 
New  York.  It  comprises,  in  effect,  a  resistance  furnace 
process,  and  the  ores  capable  of  treatment  by  it  are  known 
as  "  mispickel,"  or  arseno-pyrite  ores,  which  also  contain 
ores  of  gold,  silver,  and  other  metals  of  value.  They  are 
very  rich  in  arsenic,  averaging  46  per  cent,  by  weight  of  that 
metal,  which  exists  in  the  form  of  sulph-arsenide  of  iron 
(FeS2+FeAs2). 

In  brief,  the  process  of  reduction  consists  in  heating  the 
ore  electrically,  in  a  closed  furnace,  from  which  atmospheric 
oxygen  is  hermetically  excluded.  The  iron  combines  with 
the  sulphur,  forming  ferric  and  ferrous  sulphides,  which 
are  thrown  down  in  the  form  of  a  fused  matte,  and  include 
the  precious  metals ;  the  arsenic  itself  is  liberated  as  a  heavy 
metallic  vapour,  and  collected  in  suitable  condensers  as  a 
fine,  metallic  powder. 

The  process  is  carried  on  in  a  circulating  atmosphere  of 
nitrogen  gas,  formed,  in  the  first  place,  from  the  atmosphere 
by  extracting  the  oxygen,  by  combination  with  a  small 
quantity  of  arsenic  vapour,  to  form  the  oxide.  Once  pro- 
duced in  this  manner,  the  same  volume  of  nitrogen  is,  by 
circulation,  used  repeatedly  in  the  furnace. 

The  general  construction  of  the  latter  is  delineated  in 
Fig.  34,  where  F  is  the  furnace  proper,  with  a  refractory 
hearth  or  lining  R  of  fire-brick,  in  which  are  embedded 
the  two  cast-iron  electrodes  E  E. 

A  central  hopper  H  serves  for  the  introduction  of  the 
ore,  but,  at  the  same  time,  prevents  ingress  of  air.  M  is 
the  mass  of  fused  ore,  which  constitutes  the  resistance  path 
between  the  electrodes  ;  C  C  C  C  are  condensers,  with 
bottom  traps  t  t,  in  which  the  powdered  arsenic  collects 
and  is  removed.  The  tube  T  completes  the  circulatory 
system  for  the  nitrogen  gas,  which  is  kept  in  motion  by  a 
mechanically  driven  blower  B.  This  latter  is  reversible, 
such  that  when  one  set  of  condensers  becomes  heated,  the 

147 


ELECTRIC   FURNACES    AND 

current  of  gas  may  be  reversed,  and  the  heat  energy,  thus 
stored  up,  utilized  for  maintaining  the  general  temperature 
of  the  furnace,  which  would  otherwise  tend  to  fall. 


FIG.  34. 

An  exhaustive  test  was  conducted  on  an  experimental 
furnace  of  this  type  by  Mr.  Carl  Hering,  the  results  of  which 
were  detailed  in  the  Electrical  World,  April  27,  1901.  The 
following  essential  facts  are  extracted  therefrom. 

The  process,  owing  to  the  small  size  of  furnace  employed, 
was  naturally  wasteful  of  energy,  but,  by  measurement 
of  some  losses,  and  computation  of  others,  a  fair  estimate 
of  the  probable  cost  of  reduction  in  a  larger  furnace  was 
arrived  at. 

An  alternating  current  of  8,000  to  10,000  amperes  at  a 
periodicity  of  120,  was  used,  the  electrodes,  which,  as 
already  stated,  were  of  cast  iron,  being  about  six  square 
inches  in  cross-sectional  area,  and  rather  long. 

The  losses,  which  totalled  more  than  half  the  energy 
supplied  to  the  furnace,  were  due  to  several  contributory 
causes,  viz.,  skin  effect,  hysteresis,  resistance,  Foucault,  or 
"  eddy  "  currents,  and  conduction.  The  losses  in  leads  alone, 
from  the  secondary  of  the  transformer  to  the  furnace  ter- 
minals, amounted  to  44  kilowatts,  whilst  9  to  10  kilowatts 
were  lost  by  radiation  and  conduction. 

In  one  trial  90  kgs.  of  ore  were  supplied  to  the  furnace  in 
the  hour,  the  power  consumed  in  the  conversion  being  about 

148 


THEIR    INDUSTRIAL    APPLICATIONS 

105  k.w.  ;  the  current  varied  from  4,000  to  8,400  amperes, 
and  the  voltage  from  22  to  12,  representing  a  rate  of  approx- 
imately 1,140  k.w.  hours  per  metric  ton  of  ore. 

According  to  Mr.  Hering,  it  is  quite  safe  to  assume  that 
in  a  large,  well-designed  furnace,  the  engine  power  required 
in  the  reduction  process  would  not  be  more  than  1,000  k.w. 
hours  per  metric  ton  of  ore. 

The  theoretical  heat  energy  required  has  been  variously 
estimated  at  from  200  to  400  k.w.  hours  per  ton,  which 
points  a  margin  for  improvement. 

The  patent  rights  in  the  Westman  process  are  the  property 
of  the  Arsenical  Ore  Reduction  Company  of  Newark,  New 
Jersey,  who  are  applying  it  to  the  large  deposits  of  ore  in 
what  is  known  as  the  Big  Dan  claim  in  Ontario,  recently 
acquired  by  them. 

The  following  extract  from  Mr.  Hering' s  original  article 
contains  some  general  information  acquired  during  the 
tests,  which  should  prove  useful  in  the  design  of  electric 
furnaces  generally. 

"  Most  of  the  losses  point  to  the  importance  of  using 
continuous  currents,  if  possible,  as  it  is  very  difficult  to 
lead  such  very  large  alternating  currents  through  conductors. 
When,  however,  alternating  currents  must  be  used  to 
avoid  electrolysis,  as  is  often  the  case,  then  many  difficulties 
are  reduced  by  proportioning  the  furnace  so  that  the  current 
is  as  small  as  possible  and  the  voltage  as  great  as  possible  ; 
i.e.,  the  resistance  column  of  the  material  should  be  made 
as  long,  and  as  small  in  cross-section,  as  the  circumstances 
permit.  The  loop  formed  by  the  alternating  current  circuit 
should  have  as  small  an  area  as  possible,  so  as  to  diminish 
the  induction.  The  leads  should,  of  course,  be  made  as 
short  as  possible,  every  inch  saved  in  length  being  important. 
The  transformer  should  be  placed  within  as  few  inches  of  the 
furnace,  as  possible.  Those  parts  of  the  conductors  which 
are  unavoidable,  as,  for  instance,  where  they  pass  through 
the  walls  of  the  furnace,  should  be  made  of  insulated  lamina- 

149 


ELECTRIC    FURNACES    AND 

tions  alternately  of  opposite  polarity,  otherwise  the  skin 
and  inductive  effects  will  become  important.  For  these 
parts,  the  best  electrically  conducting  material  should  be 
used,  so  as  to  reduce  the  cross-section  as  much  as  possible, 
as  such  large  pieces  of  metal  conduct  considerable  heat 
away  from  the  interior  of  the  furnace.  The  frequency 
should  also  be  made  as  low  as  possible  when  such  very  large 
conductors  have  to  be  used. 

"  Metallic  casings  of  the  furnace  should  be  avoided, 
particularly  if  of  iron.  If  bands  are  necessary,  they  should 
be  made  of  a  non-conducting  material,  or  have  insulated 
joints  in  them  to  prevent  closed  circuits  in  the  neighbour- 
hood of  the  large  alternating  field  necessarily  produced 
in  the  part  of  the  circuit  in  the  furnace  itself.  These  are 
some  of  the  considerations  underlying  the  design  of  large 
alternating  current  resistance  furnaces. 

"  The  heat  led  off  through  the  walls  of  the  furnace,  which 
was  about  one  metre  cube,  amounted  to  about  5  k.w., 
the  inner  temperature  being  from  1,000°  to  1,200°C.=  1,832° 
to  2,192°F.,  that  necessary  for  the  vaporization  of  arsenic 
being  only  450°C.  =  842°F.  The  channel  for  the  liquid 
matte  was  about  50  c.m.  long,  and  10  c.m.  wide.  This 
loss,  which  is  not  large  for  a  furnace  of  about  150  H.P.,  could 
be  diminished  only  by  having  thicker  walls,  but  it  becomes 
relatively  less  the  larger  the  furnace. 

"  Theoretically,  the  following  relations  can  be  shown 
to  exist  for  different  sizes  of  furnace,  the  assumption  for 
enabling  a  general  law  to  be  stated  being,  that  the  furnace 
is  a  hollow  sphere  with  relatively  thick  walls,  and  that  the 
temperature  of  the  outside  surface  remains  the  same.  The 
capacity,  or  interior  volume  increases  as  the  cube  of  the 
inner  diameter.  The  thickness  of  the  walls  will  increase 
with  the  square  root  of  this  diameter,  and  the  radiation 
losses,  per  unit  volume  of  the  capacity,  or  interior  space, 
will  diminish  in  inverse  proportion  to  the  square  of  the 
diameter.  That  is,  for  twice  the  inside  diameter,  the  capa- 

150 


THEIR    INDUSTRIAL   APPLICATIONS 

city  becomes  eight  times  as  great,  the  walls  1*4  times  as 
thick,  and  the  radiation  loss  per  unit  volume  of  the  inside 
becomes  only  one  quarter  as  great,  showing  the  great  ad- 
vantage of  larger  furnaces  in  diminishing  this  loss.  For 
rectangular  furnaces,  especially  if  quite  long,  these  rela- 
tions will  not  be  quite  as  favourable,  and  these  general 
laws  then  apply  only  approximately. 

"  Heating  the  material  quickly,  i.e.,  making  each  particle 
pass  through  the  process  as  quickly  as  is  consistent  with  the 
proper  operation,  will,  of  course,  reduce  the  size  of  the 
furnace  for  the  same  output,  but,  assuming  that  a  certain 
definite  number  of  heat  units  are  required  per  ton  of  material, 
as  is  generally  the  case,  the  larger  furnace  would  require 
the  smaller  current.  Both  should  therefore  be  considered 
in  designing  a  furnace. 

"  In  all  electric  furnaces,  the  fire-brick  lining,  when  very 
hot,  becomes  a  conductor,  a  quality  which  is  made  use 
of  in  the  Nernst  lamp.  In  resistance  furnaces,  this  should 
be  taken  into  consideration,  as  it  lowers  the  resistance 
between  the  electrodes,  and  necessitates  a  greater  current, 
at  a  lower  voltage,  to  produce  the  same  heating  effect. 
This  means  that  greater  flexibility  in  the  regulating  apparatus 
is  required.  The  heat  generated  in  this  lining  is  not  lost, 
except  in  so  far  as  it  diminishes  the  thickness  of  the  heat 
insulating  walls  of  the  furnace.  The  conducting  of  the 
lining  can  be  prevented  only  by  keeping  it  cool,  which  is 
wasteful." 

Zinc. — The  electrical  distillation  of  metallic  zinc  from 
its  ores  was  a  problem  attacked  by  Messrs.  Cowles  Bros, 
in  the  early  eighties,  the  original  type  of  resistance  furnace, 
invented  by  them  for  this  purpose,  being  depicted  in  Fig.  35, 
where  F  is  the  furnace  proper,  constructed  of  fire-clay, 
in  cylindrical  form,  and  embedded  for  heat  conserving  pur- 
poses in  a  refractory  non-conducting  bed  B  of  considerable 
thickness.  The  back  of  the  furnace  consisted  of  a  carbon 
plate  or  disc  C,  which  also  constituted  a  terminal  elec- 


ELECTRIC    FURNACES    AND 


trode,  the  other  taking  the  form  of  a  graphite  crucible  G, 
which  served  the  treble  purpose  of  electrode,  removable 

cover,  or  plug, 
and  condensing 
chamber  for  the 
metallic  zinc, 
which  distilled 
over  into  it 
through  the 
orifice  o.  It  was 
closed  by  a  lid 
L,  and  fitted  with 
FIG.  35.  an  outlet  pipe 

P  for  the  escape 

of   the   gases   generated.      The   resistance  heating  column 
was  constituted  by  the  mass  of  ore  R  itself. 

It  is  probable  that  the  practical  difficulties  mentioned  in 
connexion  with  resistance  furnaces  in  the  introductory 
chapter  of  this  book  militated  against  the  adoption  of  this 
furnace  on  anything  like  a  commercial  scale. 

De  Laval's  furnace  for  the  distillation  and  reduction  of 
the  ores  of  volatile  metals,  such  as  zinc,  is  adapted  for  use 
on  either  the  arc  or  resistance  principles,  as  circumstances 
may  determine. 

It  is  represented,  in  sectional  elevation  by  Fig.  36,  and 
is  so  constructed  that  the  charge  does  not  come  into  direct 
contact  with  the  arc  or  heated  resistance,  but  passes  gradu- 
ally beneath  it.  under  the  action  of  a  reciprocating  feed 
arrangement,  and  receives,  by  radiation,  a  gradually  aug- 
mented supply  of  heat. 

The  apparatus  consists  of  a  refractory  structure  F  hav- 
ing the  form  shown  in  the  figure,  a  feed  hopper  H  com- 
bined with  a  reciprocating  piston  P,  and  an  outlet  0. 
A  is  the  arc,  or  heated  resistance  as  the  case  may  be,  the 
gradations  of  heat  from  which  are  secured  by  the  contour 
of  the  charge  ;  this  latter,  under  the  influence  of  the  reci- 

152 


THEIR    INDUSTRIAL   APPLICATIONS 


procating  feed,  assumes  the  slope  shown  ;  it  thus  receives  a 
preliminary  moderate  heating  at  the  apex  A  of  the  mass, 
which  gradually 
increases  in  in- 
ten sity  as  it 
moves  forward 
under  the  source 
of  heat,  the  pro- 
cess being  finally 
concluded  im- 
mediately below  pIG 
the  latter. 

A  steady  reaction  is  thus  secured  without  a  too  violent 
liberation  of  gas. 

The  process,  as  applied  to  the  distillation  of  metallic 
zinc  from  zinc  lead  ores,  consists  in  introducing  the  pul- 
verized ore,  in  stack  form,  as  illustrated  above.  The  radiant 
heat  of  the  arc,  struck  between  two  lateral  electrodes, 
causes  the  non-volatile  constituents  of  the  charge  to  melt 
and  flow  down  into  the  well  of  the  hearth,  whence  they 
are  tapped  off  in  the  usual  manner  ;  fresh  surfaces  of  the 
sloping  stack  are  thus  continually  exposed  to  the  arc  as  the 
fusion  proceeds.  The  volatilized  zinc,  together  with  cer- 
tain gases,  passes  off  through  the  outlet  shown,  and  is 
suitably  collected  and  condensed. 

To  eliminate  the  sulphur  in  an  untreated  zinc  sulphide 
the  inventor  suggests  mixing  iron  ore  with  the  charge,  prior 
to  its  introduction  into  the  furnace. 

Messrs.  0.  W.  Brown  and  W.  F.  Oesterle  have  taken  out 
a  patent  for  the  electrical  smelting  of  blended  zinc  sulphides, 
one  of  the  claims  being  that  valuable  by-products  (calcium 
carbide  and  carbon  bisulphide)  are  formed  in  the  process. 
Coke,  or  carbon,  is  mixed  with  the  ore,  and  the  mixture 
heated  in  an  electric  furnace  to  a  temperature  "  sufficiently 
high  to  produce  the  desired  products."  Metallic  zinc 
separates  out,  is  volatilized  and  collected  by  condensation 

153 


ELECTRIC   FURNACES   AND 

in  the  usual  manner,  whilst  the  carbon,  calcium,  and 
sulphur,  also  present  in  the  ore,  combine  to  form  the  above- 
named  by-products. 

These  details  furnished  by  the  patent  specifications  are 
somewhat  meagre,  and  there  is  no  mention  of  its  practical 
application  on  an  industrial  scale. 

Salgues  describes  (Paper  before  the  Societe  des  Ingenieurs 
Civils  de  France,  1903)  a  process  of  treating  zinc  ores  in 
the  electric  furnace. 

The  ore,  in  the  form  of  the  oxides  and  sulphides,  is  mixed 
with  a  suitable  flux,  and  subjected  to  the  action  of  the 
furnace  in  which  it  is  fused,  and  a  reaction  started,  either 
in  itself,  or  with  suitable  reducing  agents,  carbon,  iron,  etc. 
The  resulting  slag  contains  practically  no  zinc,  whilst  the 
latter  is  either  tapped  off,  or  distils  over  according  to  the 
conditions  of  operation. 

Treating  ores  containing  40  per  cent,  metallic  zinc,  in 
furnaces  of  100  k.w.  capacity,  nearly  5  kgs.  of  metal  per 
k.w.  day  have  been  obtained. 

The  operation  is  conducted  in  a  closed  furnace,  and  has 
been  on  practical  trial  at  a  carbide  factory  at  Campagna,  in 
the  French  Pyrenees. 

Dorsemagen  has  devised  a  process  for  the  electric  furnace 
reduction  of  siliceous  zinc  ore,  the  products  being  metallic 
zinc  and  carborundum  (silicon  carbide).  A  mixture  of  the 
ore  with  carbon  is  heated  in  an  ordinary  electric  furnace, 
with  carbon  electrodes,  the  result  being  that  silicon  carbide 
is  formed,  whilst  the  metallic  zinc  distils  over. 

An  analogous  process  is  due  to  Borchers  and  Dorsemagen, 
and  is  employed  in  the  treatment  of  compound  ores  con- 
taining both  iron  and  zinc,  the  products  being  ferro-silicon 
and  zinc.  The  process  is  practically  identical  with  the 
foregoing. 

An  Italian  process  of  zinc  smelting  in  the  electric  furnace, 
invented  by  Casaretti  and  Bertani,  is  worked  by  an  electro- 
metallurgical  company.  One  kilogramme  of  zinc  is  pro- 

154 


THEIR    INDUSTRIAL    APPLICATIONS 

duced  per  2  H.P.  hours,  and  the  consumption  of  coal  in 
the  furnace  is  15  kgs.  per  100  kgs.  of  ore. 

Chromium. — Herr  Aschermann  has  succeeded  in  pre- 
paring chromium  in  the  electric  furnace.  He  uses  a  gas- 
tight  steel  structure,  containing  a  graphite  crucible,  which 
forms  the  hearth  of  the  furnace,  and  into  which  passes  from 
the  outside,  a  movable  electrode.  The  raw  material  con- 
sists of  a  mixture  of  oxide  of  chromium  and  sulphide  of 
antimony,  in  the  proportion  of  ten  parts  to  twenty- three. 
This  is  placed  in  the  crucible,  and  the  furnace  closed,  where- 
upon a  current  of  about  twenty  amperes  is  passed  through, 
and  suffices  to  fuse  the  charge. 

Alloys  of  chromium  and  antimony  result  from  the  fusion, 
whilst  an  amorphous  mass  of  the  suphides  and  oxides  of 
antimony  remains  on  the  upper  walls  of  the  crucible.  The 
antimony  may  be  driven  off  in  its  entirety  by  reheating, 
whilst  the  carbon,  an  appreciable  quantity  of  which  is 
absorbed  and  dissolved  by  the  chromium,  separates  out  as 
graphite  on  cooling. 

The  process  was  exploited  at  Cassel,  Germany,  in  1897-98. 

Molybdenum. — Can  be  prepared  in  a  similar  manner  from 
its  dioxide  (Mo02)  by  heating  the  latter  in  conjunction 
with  a  small  percentage  of  carbon. 

Tungsten. — Is  prepared  by  reducing  tungstic  acid  (H2WO4), 
with  a  small  percentage  of  carbon,  in  the  electric  furnace.  If 
the  carbon  be  in  excess  or  the  mass  too  thoroughly  fused,  a 
cast  metal  or  carbide  is  the  result.  Care  must  therefore  be 
exercised,  in  preparing  pure  metallic  tungsten,  to  regulate 
the  temperature,  and  allot  the  proportion  of  carbon  required 
for  the  reduction  most  carefully. 

Nickel. — An  electric  furnace  process  for  the  direct  pro- 
duction of  nickel  from  its  ores  has  been  exploited  at  Sault 
Ste.  Marie,  Ontario,  U.S.A. 

A  revolving  electric  furnace,  designed  by  F.  H.  Clergue, 
was  employed,  in  which  the  ores  were  smelted  by  the  heat 
of  the  arc.  A  ferro-nickel  alloy  was  said  to  be  obtained  in 

155 


ELECTRIC    FURNACES    AND 

one  operation,  a  sample  of  which,  submitted  to  Messrs. 
Krupp,  of  Essen,  gave  great  satisfaction,  and  is  rumoured 
to  have  led  to  the  placing  of  a  large  order  for  the  alloy. 

Sodium. — A.  H.  Cowles  has  taken  out  a  patent  on  an 
electric  furnace  process  for  smelting  or  reducing  sodium 
aluminate.  To  this  end,  the  latter  is  broken  up  and  intim- 
ately mixed  with  granular  carbon,  and  the  mixture  subjected 
to  heat  in  a  closed  electric  furnace.  Metallic  sodium  is 
liberated  in  the  form  of  vapour,  and  passes  over  to  be 
collected  and  condensed  in  a  suitable  receiver,  whilst 
the  aluminium  of  the  compound  combines  with  the  carbon 
to  form  aluminium  carbide,  which  can  be  tapped  off  from 
the  furnace  hearth. 

Alloys  of  Iron  and  Steel. — In  his  presidential  address  to  the 
Society  of  Chemical  Industry,  in  July,  1901,  Mr.  J.  W.  Swan 
touched  upon  the  growing  importance  of  this  industry,  not 
only  from  the  steel  manufacturer's  point  of  view,  but  also 
as  an  alternative  industry  to  which  many  idle  carbide 
plants  might,  for  the  nonce,  be  applied. 

Chromium  and  chrome  iron  are  being  made  at  Essen  by  the 
Goldschmidt  process,  by  the  Willson  Company  in  America, 
and  by  several  of  the  French  metallurgical  companies. 
Ferro-silicon  is  being  produced  at  Meran,  in  the  Austrian 
Tyrol,  and  also  at  a  few  of  the  carbide  works  in  France. 

According  to  Mr.  Swan,  the  raw  ingredients  consist  of 
scrap  iron,  quartz  and  coke.  The  daily  yield  of  each 
furnace  is  1,200  kgs.,  and  the  product  contains  77-5  per  cent, 
iron,  and  21-5  per  cent,  silicon,  and  costs,  at  Meran,  £8  per 
ton.  The  yield,  in  the  electric  furnace  is  one  ton  per  5,000 
k.w.  hours. 

Ferro-titanium  is  produced  by  heating  together  scrap  iron, 
titaniferous  ore,  and  aluminium,  in  an  electric  furnace. 
Over  30,000  H.P.  were  available  in  1901  for  the  manufacture 
of  these  alloys  in  the  electric  furnace. 

In  this  connexion,  it  may  be  mentioned  that  the  Willson 
Aluminium  Company  recently  installed  a  3,000  H.P.  plant 

156 


THEIR    INDUSTRIAL   APPLICATIONS 

for  the  manufacture  of  ferro-chrome,  at  Great  Kanawha 
Falls,  thirty-six  miles  above  Charleston,  W.Va.,  U.S.A. 
The  chrome  ore  used  in  the  manufacture  is  imported  from 
Australia  and  Asia  Minor,  and  the  resultant  alloy  contains 
as  much  as  70  per  cent,  chromium. 

In  1901,  the  entire  output  of  the  plant  was  being  taken  by 
the  Carnegie  and  Bethlehem  Steel  Companies,  who  employed 
it  for  hardening  armour  plates  for  the  U.S.  Navy. 

Gin  (U Industrie  Electrique,  April  25,  1901),  gives  some 
interesting  statistics  relating  to  the  thermo-electric  manu- 
facture of  ferro-silicon  at  Meran.  The  materials  and  pro- 
portions used  were — 

Iron  scale  (forge)       .....      1,000  parts. 

Quartz 410     „ 

Coke 398     „ 

The  respective  percentages  of  useful  material  were :  iron, 
71-9  per  cent.  ;  silica,  91-3  per  cent. ;  and  carbon,  63-9  per 
cent,  of  the  raw  material.  The  normal  consumption  of 
energy  was  at  the  rate  of  seventy  watts  per  square  centimetre 
of  section.  The  material  was  cast  in  lots  of  776  kgs.,  an 
interval  of  15  hours  separating  two  consecutive  casts.  The 
efficiency  of  the  process  was  80  per  cent.,  and  the  yield, 
200  grammes  per  k.w.  hour.  The  fusion  temperature 
varies  from  1,130°  to  1,400°  C.=  2,066°  to  2,552°F. 

The  resultant  product  had  the  following  percentage  com- 
position— 

Silicon  .          .          .          .          .          .21-45  per  cent. 

Iron 77-50     „       „ 

The  working  costs  at  that  period  were  in  the  neighbourhood 
of  200  francs  per  metric  ton,  or,  in  English  currency,  £7  18s, 

In  the  same  article,  M.  Gin  describes  a  method  of  manu- 
facturing ferro-silicon  from  steel  furnace  slags.  The  latter, 
which,  in  this  particular  instance,  was  obtained  from  a 
Martin  furnace,  had  the  following  composition — 

157 


ELECTRIC   FURNACES   AND 


Silica 
Alumina 
Ferrous  oxide 
Manganese  monoxide 
Lime,  magnesia,  etc. 


50-42    per  cent. 


2-26 
34-1 
9-42 
3-30 


The  above,  mixed  with  coke,  in  the  proportion  of  1,680  kgs. 
of  slag  to  600  kgs.  of  coke,  containing  80  per  cent,  carbon, 
yielded  a  product  which  analyzed  as  follows— 


Silicon 
Iron    . 
Manganese 
Carbon 
Miscellaneous 


29-64    per  cent. 

53-7 

13-18 


vO 


2-96 


The  yield  consisted  of  4,090  kgs.  in  110  hours,  the  current 
required  being  6,950  amperes  at  29-1  volts,  or  an  energy  con- 
sumption of  5,380  k.w.  hours  per  metric  ton. 

Ferro-silicon  is  a  far  more  active  agent  than  carbon  in 
the  process  of  steel  manufacture.  The  combustion  of  1  per 
cent,  evolves  heat  to  the  extent  of  7,830  calories,  as  compared 
with  2,473  calories  for  the  combustion  of  a  similar  quantity 
of  carbon. 

According  to  Keller  (Paper  before  Iron  and  Steel  Institute, 
1903)  the  degree  of  purity  attainable  with  ferro-silicon 
manufactured  in  the  electric  furnace  is  governed  by  the 
percentage  of  silicon  present ;  in  other  words,  the  larger  the 
silicon  content,  the  greater  the  purity  of  the  alloy. 

He  explains  this  by  the  fact  that  it  is  the  iron  itself  which 
is  responsible  for  the  introduction  of  impurities,  and  that, 
owing  to  the  higher  temperatures  necessary  for  the  produc- 
tion of  alloys  with  a  large  silicon  content,  the  impurities  are 
either  volatilized,  or  eliminated  by  secondary  reactions. 

He  has  obtained  the  following  analysis  for  a  50  per  cent, 
ferro-silicon — 

Phosphorus  .          .          .          .          .          .        0-02  per  cent. 

Sulphur         .          .          .          .         V         .        Trace 

Carbon  .  •„          .          .          .  „ 

Actual  working  results  have  demonstrated  that  the  energy 

158 


THEIR    INDUSTRIAL    APPLICATIONS 

required  for  the  production  of  one  ton  of  30  per  cent,  ferro- 
silicon  in  the  electric  furnace  is  3,500  k.w.  hours.  Messrs. 
Keller,  Leleux,  &Co.,in  their  works  at  Livet,  Isere,  France, 
have  an  available  total  of  15,000  H.P.  It  has  been  found 
practicable,  with  an  expenditure  of  4,000  H.P.,  to  turn  out 
twenty  tons  of  30  per  cent,  ferro-silicon  per  day,  whilst  alloys 
with  as  high  a  silicon  content  as  70  to  80  per  cent,  have  been 
manufactured.  The  furnaces  employed  at  the  Livet  works 
are  of  the  resistance  type,  and  are  of  650  H.P.  capacity. 

Ferro-Chrome.—The  Willson  Company,  in  1898,  were 
stated  to  be  manufacturing  ferro-chrome  at  the  rate  of  60 
tons  per  month. 

Aluminium  Alloys. — The  Cowles  furnace,  for  the  manu- 
facture of  aluminium  alloys,  consisted  of  a  fire-brick  struc- 
ture, with  massive  fire-clay  lid,  in  which  latter,  orifices  were 
left  for  the  escape  of  the  gases.  The  electrodes  entered 
through  two  opposite  walls  at  an  angle,  and  consisted  of 
bundles  of  carbon  rods  mounted  in  massive  metal  caps,  the 
material  of  which  was  a  constituent  of  the  alloy  under 
preparation,  in  order  to  guard  against  contamination  of  the 
product  in  the  event  of  fusion,  which  sometimes  occurred 
towards  the  end  of  a  run.  The  electrodes  entered  through 
tubular  conduits,  and  were  provided  with  screwed  rod 
adjustment. 

The  furnace  was  lined  interiorly  with  broken  charcoal, 
which  latter  was  protected  from  any  tendency  to  agglom- 
erate under  the  intense  heat  of  the  furnace,  by  a  previous 
immersion  in  lime  paste,  which  coated  each  particle  and 
separated  it  from  its  neighbour. 

In  this  connexion  it  is  interesting  to  note  that  here  were 
the  elements  necessary  for  the  production  of  calcium 
carbide,  then  a  comparatively  unknown  compound  ;  and, 
indeed,  it  is  probable  that  calcium  carbide,  in  minute 
quantities,  was  frequently  formed,  incidentally,  during  the 
action  of  this  early  Cowles  furnace. 

Alumina,   in  the   form   of  corundum   (crystallized)   was 

159 


ELECTRIC   FURNACES    AND 

employed  in  this  process,  the  initial  charge  consisting  of 
15  kgs.  corundum,  30  kgs.  of  granulated  copper,  and  suffi- 
cient carbon  to  impart  the  necessary  conductivity  to  the 
mixture.  The  current  required  for  the  operation  was  3,000 
amperes  at  50  volts,  which  was  maintained  throughout  the 
run,  the  electrodes  being  adjusted  according  to  the  variation 
in  electrical  resistance  of  the  mass  under  treatment.  Each 
run  lasted  from  two  to  three  hours,  the  reaction  which 
took  place  being  represented  by  the  equation  — 

3C  =  3CO+A1. 


The  carbon  monoxide  gas  formed  was  burnt  under  a 
chimney,  and  the  resultant  products  of  combustion  carried 
through  a  special  flue,  in  which  they  deposited  any  metallic 
particles  carried  over  by  them  from  the  furnace. 

The  product  contained  from  15  to  20  per  cent,  of  alumin- 
ium, and  the  output  of  the  later  trials  at  Milton  were  33 
grammes  per  k.w.  hour,  as  against  a  theoretical  yield  of 
152  grammes,  or  an  efficiency  of  only  22  per  cent. 

This  aluminium  bronze,  or  aluminium  gold,  as  it  is  some- 
times termed,  consists  of  one  part  aluminium  and  nine  parts 
copper. 

The  introduction  of  the  Heroult  and  Hall  processes  for  the 
manufacture  of  pure  aluminium  have  entirely  superseded  the 
Cowles  process  for  the  production  of  aluminium  alloys,  the 
pure  metal  being  first  obtained,  and  then  alloyed  in  the 
desired  proportion,  thus  yielding  a  much  purer  and  more 
homogeneous  product. 

A  later  process,  patented  in  1901  by  A.  H.  Cowles,  for 
the  manufacture  of  aluminium  bronze  in  the  electric 
furnace,  though  far  from  efficient,  presents  several  novel 
points.  The  furnace  consists  of  a  porous  carbon  crucible, 
hermetically  sealed  by  a  close-fitting  lid,  through  which 
passes  a  carbon  rod.  This  latter,  and  the  crucible  itself, 
constitute  the  two  electrodes.  Volatile  products,  e.g.  sodium, 
resulting  from  the  reduction  of  sodium  aluminate  in  the 

1  60 


THEIR   INDUSTRIAL   APPLICATIONS 

crucible  by  carbon,  pass  through  the  porous  walls  of  the 
latter,  under  pressure  of  the  gases  produced  in  the  reaction 
and  are  condensed  on  the  inner  walls  of  a  cooling  tank,  or 
water  jacket,  which  surrounds  the  crucible,  and  with  it 
forms  an  annular  space,  in  which  the  volatile  product  is 
collected.  The  aluminium  carbide  remains  behind  in  the 
crucible,  or,  if  copper,  or  other  metal  be  employed,  an  alu- 
minium alloy  is  the  result. 

In  order  to  prevent  clogging  of  the  pores  in  the  walls  of 
the  crucible  a  very  high  temperature  is  necessary,  a  fact 
which  would  presumably  detract  from  the  efficiency  of  the 
process. 

The  Comminution,  or  Pulverization  of  Metals,  with  or 
without  the  subsequent  production  of  their  oxides  by  com- 
bustion in  oxygen,  is  a  branch  of  metallurgy  to  which  the 
electric  furnace,  duly  modified,  is  admirably  adapted. 

The  general  method  of  procedure  consists  in  heating  the 
metal,  either  by  means  of  an  arc  or  resistance  furnace,  to 
the  temperature  of  volatilization ;  the  resulting  vapour 
burns  in  air  or  oxygen,  and  the  oxide  of  the  metal  is  pro- 
duced. In  the  event  of  comminution  of  the  metal,  pure  and 
simple,  being  required,  the  operation  is  carried  out  in  a 
neutral  atmosphere. 

One  of  the  earliest  applications  of  the  electric  furnace  to 
these  requirements  was  made  in  1896  by  the  Societe  Civile 
d'Etudes  du  Syndicat  de  1'Acier  Gerard,  of  Paris,  who  took 
out  a  patent  on  a  process  for  the  production  of  steel  from 
pig  iron.  In  the  main,  the  process  consisted  in  pulverizing 
the  metal,  and  afterwards  subjecting  it  to  an  air  blast,  which 
resulted  in  the  oxidation  of  silicon,  sulphur,  phosphorus, 
and  carbon,  and  in  due  course  the  conversion  of  the  iron 
into  steel. 

To  effect  the  necessary  pulverization,  an  arc  was  suggested, 
the  primarily  fused  metal  being  poured,  in  a  falling  stream, 
between  the  two  carbons  and  consequently  through  the  heat 
zone  of  the  arc,  after  which  it  passed  through  an  air  blast, 

161  M 


ELECTRIC   FURNACES    AND 


and  was  subsequently  collected  in  the  hearth  of  the  fur- 
nace. 

In  a  modified  method,  the  metal  was  heated  in  a  resistance 
furnace,  having  water-cooled  terminals,  and  oxidation  of 
the  vapour  effected  by  a  blast  of  air  projected  against  the 
surface  of  the  molten  mass  at  the  point  of  maximum 
temperature. 

The  process,  patented  in  1902  by  C.  S.  Lomax,  for  the 
manufacture  of  the  oxides  of  lead  and  tin,  is  almost  identical 
with  the  above,  the  general  principle  of  furnace  and  operation 
being  illustrated  in  Fig.  37,  where  H  is  a  shallow 
hearth  with  enlarged  or  expanded  end  cavities,  the  metal 
in  which  remains  cooler  by  virtue  of  their  greater  cross- 
section  and  consequent  carry- 
ing capacity,  and  in  which  ter- 
minal electrodes  are  inserted 
for  connexion  to  the  source  of 
current.  P  is  a  supply  pipe, 
for  the  delivery  of  air  under 
pressure  through  a  series  of 
branch  nozzles  •  n  at  or  near 
the  surface  of  the  molten  metal 
in  H.  The  oxides,  thus  formed, 

pass  over,  under  direction  of  the  controlling  air  blast  and 
cover  C,  into  a  receiving]  chamber  R,  where  they  are 
collected. 

It  is  claimed  for  this  furnace  that  pure  dioxide  of  tin  may 
be  produced  by  the  action  of  an  air  blast,  the  temperature 
of  which  has  been  primarily  raised  to  400°C.—  752°F.,  the 
molten  mass  being  at  1,200°C.=2,192°F.,  whilst,  under 
similar  conditions,  but  with  a  cold  air-blast,  putty  powder, 
a  mixture  of  the  dioxide  and  monoxide  of  tin,  is  formed. 
In  the  manufacture  of  lead  oxides  a  cold  air  blast  is  employed. 
M.  Paul  Bary  has  devoted  considerable  attention  to  this 
subject,  and  his  more  recent  apparatus  is  based,  in  principle, 
upon  the  volatilization  of  a  stream  of  molten  metal  carrying 

162 


FIG.  37. 


THEIR    INDUSTRIAL    APPLICATIONS 


a  current  by  the  intermittent  arc  which  follows  a  rapid  and 
continuous  series  of  interruptions. 

It  is  a  well  known  fact  that  if  a  current  of  certain  density 
be  passed  through  a  metallic  film,  the  continuity  of  the  latter 
is  momentarily  destroyed,  and  immediately  restored  again 
at  a  rate  amounting  to  some  hundreds  of  interruptions  per 
second  ;  it  is  upon  this  phenomenon  that  M.  Bary  has  based 
the  construction  of  his  latest  apparatus,  which  presents  several 
points  of  interest. 

A  sectional  elevation  of  the  furnace  is  represented  in 
Fig.  38  ;  it  comprises 
an  upper  chamber  A 
divided  from  a  lower 
receiving  chamber  B 
by  a  horizontal  par- 
tition p.  The  con- 
struction is  circular, 
and,  through  equi- 
distant points  around 
the  circle  formed  by 
the  partition  p,  pass, 
vertically,  a  series 
of  small  tubes  n  n, 
extending  upwards 

above  the  surface  of  the  molten  metal  in  A,  but  provided 
with  side  perforations  at  a  a  to  permit  the  passage  of  the 
metal  into  the  lower  chamber  B.  At  their  lower  extremities 
s  s,  which  extend  into  B,  the  tubes  n  converge  into  fine 
nozzles,  which  serve  to  concentrate  the  falling  streams  upon 
a  series  of  metal  buttons  m  m  placed  immediately 
beneath  them.  An  insulating  partition  D  is  introduced 
just  above  the  line  of  nozzles,  which  electrically  isolates  the 
upper  portion  A  from  the  lower  B,  the  only  connexion 
between  the  two,  being  through  the  tubes  n,  nozzles  s, 
buttons  m,  and  the  passing  streams  of  molten  metal,  which, 
as  already  indicated,  automatically  break  up  and  reform 

163 


FIG.  38. 


ELECTRIC    FURNACES    AND 

themselves  several  hundred  times  per  second  under  the  action 
of  the  current  which  they  carry.  R  R  are  resistances  located 
between  the  upper  and  lower  chambers,  and  included  in  the 
main  circuit.  These,  heated  by  the  current,  serve  to  main- 
tain the  contents  of  both  chambers  in  a  molten  state.  The 
metallic  buttons  m,  and  the  conductors  leading  to  them, 
are  embedded  in  a  refractory  base  E,  which  slopes  towards 
the  outlet  0.  The  oxidized  products  pass  over  through 
this  outlet  into  a  suitable  receiving  chamber,  any  excess  of 
unconverted  metal  being  caught,  in  passage,  by  a  trap  T. 

F  is  an  inlet  for  the  introduction  of  the  necessary  oxidiz- 
ing gas,  and  serves  also  as  an  electrode  connexion  to  the 
external  circuit,  the  remaining  connexion  being  made  to  the 
upper  chamber  A. 

The  Bary  process  for  the  manufacture  of  stannic  acid 
comprises  a  resistance  furnace  in  which  the  tin  is  vaporized, 
and  the  resultant  vapour,  passing  through  an  orifice  in  the 
upper  part  of  the  structure,  is  ignited  by  a  blast  of  air, 
forming,  by  combustion,  dioxide  of  tin.  The  patent  is  con- 
trolled and  applied  by  the  Tin  Electro-Smelting  Co.,  Ltd.,  of 
Paris. 

The  electric  furnace  process  for  the  manufacture  of  white 
lead,  patented  by  Messrs.  Bailey,  Cox,  &  Hey,  consists  in 
striking  an  arc  between  a  tubular  electrode,  and  the  surface 
of  the  molten  lead  to  be  converted.  The  tubular  electrode 
serves  also  as  a  conduit,  through  which  is  introduced  a 
mixture  of  steam,  carbon  dioxide  gas,  and  acetic  acid 
vapour,  the  reaction  between  which,  and  the  vaporized 
lead  at  the  central  heat  zone,  results  in  the  formation  of 
commerical  white  lead. 

By  a  new  method,  pigments  of  metallic  oxides  are  pro- 
duced by  burning,  in  special  flues,  the  waste  vapours  from 
electric  reduction  furnaces.  The  varying  mixtures,  from 
different  ores,  give  a  great  variety  of  colours,  waste  is  avoided, 
and  the  products  are  in  extremely  fine  powder  without 
grinding. 

164 


THEIR    INDUSTRIAL    APPLICATIONS 


SECTION  VI 

PHOSPHORUS   MANUFACTURE   IN    THE    ELECTRIC   FURNACE 

Speaking  generally,  the  main  difficulty  experienced  in  the 
manufacture  of  phosphorus,  per  se,  in  the  electric  furnace, 
is  the  necessarily  high  temperature  at  which  the  vapour 
leaves  the  furnace  chamber.  This  vapour  was  originally 
condensed  immediately  after  leaving  the  furnace  by  means 
of  a  water  circulatory  system,  but  improvements  have  since 
been  effected  by  the  Compagnie  Electrique  du  Phosphor, 
Billaudot  &  Cie. 

In  the  method  adopted  by  this  firm,  the  vapour  is  led 
through  a  system  of  cooling  towers,  whereby  the  condensation 
is  carried  on,  by  air  cooling,  at  a  slower  rate,  and  it  is  said 
to  yield  not  only  a  better  quality  of  phosphorus,  but  also  a 
larger  quantity,  and  at  a  reduced  cost. 

In  1899,  it  was  stated  (Tatlock)  that  one-half  the  world's 
production  of  phosphorus,  approximately  1,000  tons,  was 
manufactured  by  electric  furnace  methods. 

A  process  for  the  manufacture  of  phosphorus  in  the  electric 
furnace  was  invented  independently  by  Dr.  Headman  and 
Mr.  Thos.  Parker,  in  1888. 

The  two  inventors  subsequently  combined  interests,  and 
the  Parker  furnace,  illustrated  in  Fig.  39,  was  the  outcome. 

It  consists  of  a  fire-brick  structure  F,  with  a  domed  roof, 
through  an  aperture  in  the  centre  of  which  the  raw  material 
is  fed  from  the  hopper  H  by  the  mechanically  driven  screw 
conveyor  S.  The  disposition  of  all  parts  is  such  that  air  is 

165 


ELECTRIC    FURNACES    AND 


hermetically  excluded  from  the  interior  of  the  furnace.  The 
lower  portion  of  the  structure  is  contracted  to  form  a  hearth 
A,  as  shown,  and,  through  the  side  walls  at  this  point,  are 

introduced  the  terminal 
carbon  electrodes  E  E 
in  parallel  sets,  which  serve 
to  convey  the  current  to 
the  charge,  the  furnace 
operating  on  the  resist- 
ance principle.  This  linear 
distribution  of  electrodes 
results  in  distributing  the 
heat  area,  and  rendering 
the  effect  more  uniform. 

The  two  rows  of  smaller 
electrodes  e  e,  placed  be- 
*  low  the  main  electrodes, 
suffice  to  start  the  heat- 
ing of  the  charge,  and 
bring  it  up  to  a  certain 
point,  after  which  it  is 

maintained  by  the  current  passing  between  E  E.  D  is 
a  flue  for  conducting  away  the  gases  and  vapours  formed 
during  the  process. 

The  Readman  and  Parker  process  was  perfected  commer- 
cially in  1888.  It  was  exploited  on  a  large  scale  at  the  works 
of  the  Electric  Construction  Company,  Wolverhampton, 
and  has  since  been  adopted  by  Messrs.  Albright  and  Wilson, 
at  Oldbury.  The  mineral  phosphate  is  first  pulverized,  then 
mixed  with  carbon  and  sand,  and  finally  heated  in  the 
closed  electric  furnace  described  above,  whereupon  the 
phosphorus  distils  over  and  is  collected  under  water. 

The  capacity  of  the  furnace  is  80  kgs.  of  phosphorus  per 
furnace  per  day.  The  process  is  fairly  economical,  in  that 
from  80  to  90  per  cent,  of  the  phosphorus  contained  in  the 
charge  is  recovered.  In  1898,  the  Oldbury  works  utilized 

166 


FIG.   39. 


THEIR    INDUSTRIAL    APPLICATIONS 

some  700  H.P.,  and  the  Niagara  works  300  H.P.,  in  the 
manufacture  of  this  element,  but  the  plant  and  output  have 
since  been  considerably  extended.  Phosphorus,  to  the 
amount  of  fifteen  tons  per  month,  is  said  to  be  produced  at 
Niagara  Falls  by  the  Oldbury  Chemical  Company. 

Similar  plants  are  in  existence  at  Geneva  (Switzerland), 
and  Greisheim  (Germany),  in  which  latter  country  the 
refusal  of  patent  rights  has  left  the  electric  furnace  method 
open  to  all  comers. 

The  resistance  furnace,  invented  by  H.  A.  Irvine  for  the 
electrical  manufacture  of  phosphorus,  is  closely  allied  to  the 
original  De  Laval  furnace,  described  in  the  section  on 
smelting,  in  that  the  resistance  column  is  in  a  state  of  fusion. 
The  furnace  consists  of  a  refractory  chamber,  with  a  domed 
roof,  in  the  centre  of  which  is  fitted  a  feed  hopper,  and 
through  which,  on  either  side  of  the  hopper,  descend  ver- 
tical carbon  electrodes,  their  lower  extremities  reaching  to 
within  a  short  distance  of  the  floor  or  hearth  of  the  furnace, 
which  latter,  together  with  the  side  walls,  is  composed  of 
packed  carbon. 

Tap  holes  are  provided,  whereby  the  level  of  the  molten 
mass  on  the  furnace  hearth,  and  consequently  the  cross- 
section  of  the  conducting  column  between  the  electrodes, 
is  maintained  constant.  Two  lower  horizontal  carbon 
electrodes,  projecting  through  the  furnace  walls,  on  a  level 
with  the  hearth,  also  provide  a  ready  means  of  changing 
the  direction  of  the  current  path,  if  such  be  necessary. 

The  action  is  first  started  through  a  layer  of  granular 
coke,  so  placed  as  to  bridge  the  lower  extremities  of  the 
electrodes,  and  is  subsequently  maintained  through  a  mass 
of  conducting  slag,  formed  from  the  fusion  of  the  raw 
materials.  The  charge  consists  of  a  mixture  of  phosphate 
rock,  carbon,  and  the  necessary  proportion  of  a  suitable 
flux,  and,  in  its  molten  state,  covers  the  furnace  hearth  to 
a  constant  level,  determined  by  the  aforementioned  tap 
holes.  The  unfused  charge  rests  on  the  top  of  this  molten 

167 


ELECTRIC    FURNACES    AND 

mass,  and,  as  it  melts,  flows  down  to  take  the  place  of  that 
already  fused  and  drawn  off. 

The  principal  difficulty  experienced  in  the  application 
of  furnaces  of  this  type  to  industrial  operations  on  a  com- 
mercial scale  is  that  of  finding  a  sufficiently  refractory  and 
non-conducting  lining,  which  shall,  at  the  same  time,  be 
proof  against  oxidation  by  the  furnace  contents. 

The  Machalske  electric  furnace  process  for  the  manu- 
facture of  phosphorus,  invented  by  Dr.  F.  J.  Machalske,  of 
Long  Island  City,  New  York,  and  exploited  by  the  Anglo- 
American  Chemical  Company,  is  illustrated  in  Fig.  40. 
The  furnace  consists  of  a  central  chamber,  or  crucible  C, 
36  by  12  by  18  in.,  built  up  of  carbon  blocks,  and  lined 
interiorly  with  calcined  magnesia  and  a  special  mixture, 
whilst  outside  it  is  jacketed  with  fire-clay,  red  brick, 
and  a  mixture  of  borax  and  asbestos  flour.  The  upper 
electrode  E  is  mounted  in  a  special  holder  or  clamp  A, 
and  provided  with  a  hand  wheel  and  worm  W  for  feed 
adjustment.  It  is  4  in.  in  diameter,  and  8  ft.  long.  The 
lower  electrode  E2  passes  vertically  up  through  the  floor 
of  the  furnace,  and  is  also  provided  with  a  screw  and  hand 
wheel  adjustment,  W2,  as  shown. 

The  raw  material,  or  phosphate,  is  placed  in  the  hopper 
H,  and  fed  into  the  furnace  chamber  by  the  screw  conveyor 
S.  Once  the  action  is  started  the  arc  can  be  drawn  out  to 
as  great  a  length  as  15  in. 

An  alternating  current  is  employed,  with  a  voltage 
ranging  from  30  to  120.  Each  furnace  takes  from  1,000 
to  4,000  amperes,  and  a  temperature  of  3,867°C.=  7,000°F. 
is  available  within  five  minutes  of  switching  on. 

A  molten  slag,  consisting  mainly  of  calcium  silicate,  is 
produced,  and  run  off  at  the  tap  hole  T,  whilst  the  phos- 
phorus is  driven  off  as  vapour,  and  passes,  by  way  of  the 
outlet  O,  into  suitable  condensers,  where  it  is  solidified  in 
the  form  of  dark  yellow  shavings.  These  are  subsequently 
treated  with  sodium  hypobromide,  whereby  the  red  phos- 

168 


THEIR    INDUSTRIAL    APPLICATIONS 


phorus  is  converted  into    yellow,   and    impurities  elimin- 
ated. 

The  chemical  equation  representing  the  reaction  which 
takes  place,  is  as  follows  : — 

Ca3(P04)2  +  3Si02  +  50 =3CaSi03  +  5CO  +  2P. 

The  calcium  monosilicate,  as  already  stated,  accumulates 
on  the  furnace  hearth, 
whence  it  is  run  off  in 
a  syrupy  condition. 

In  the  Machalske 
furnace,  as  described 
above,  68  kgs.  of  the 
raw  phosphate  can  be 
treated  in  a  quarter  of 
an  hour,  yielding  yellow 
phosphorus  at  3%d.  per 
pound,  reckoned  on  a 
basis  of  2d.  per  B.O.T. 
Unit. 

Two  of  these  furnaces, 
each  consuming  2,000 
amperes,  are  in  use  by 
the  Anglo  -  American 
Chemical  Company  in 
the  manufacture  of  yel- 
low and  red  phosphorus. 

Dr.  Machalske  states,  that  in  the  course  of  his  experiments 
with  the  above  process  of  phosphorus  manufacture,  he 
discovered  that,  by  means  of  an  electric  furnace,  connected 
to  special  condensing  apparatus,  chlorides  of  carbon,  more 
especially  carbon  tetrachloride,  ,  could  be  produced  by 
treating  a  mixture  of  common  salt,  carbon,  and  sand. 


169 


ELECTRIC    FURNACES     AND 


SECTION    VII 

GLASS  MANUFACTURE  IN  THE  ELECTRIC  FURNACE 

One  of  the  more  recent  applications  of  the  electric  furnace 
is  in  the  manufacture  of  glass,  a  process  which  entails  con- 
siderable expenditure  of  heat,  and  a  comparatively  clean 
source  for  the  latter,  such  that  no  impurities,  in  the  shape 
of  combustion  products,  etc.,  shall  enter  into  the  fused 
mass,  and  destroy  the  purity  and  transparency  of  the 
finished  article. 

Nernst's  discoveries  in  connexion  with  such  earths  as 
become  conductors  when  heated  to  a  certain  degree,  have 
an  important  bearing  on  the  development  of  this  industry, 
in  that  glass  itself  may  be  numbered  among  those  sub- 
stances ;  molten  glass  is,  in  point  of  fact,  an  electrolyte,  and 
thus  lends  itself  readily  to  electric  furnace  methods  of 
manufacture. 

One  of  the  earliest  electric  furnaces  for  glass  production 
was  patented  in  Germany,  in  1882,  by  Messrs.  S.  Reich  & 
Co.  It  was  of  the  resistance  type,  and  consisted  essentially 
of  a  carbon  crucible,  open  at  the  base,  and  lined  internally 
with  a  net  or  bag  of  platinum  wire. 

The  raw  material  was  fed  into  this,  and,  having  been 
fused,  by  the  heat  developed  in  the  carbon  walls,  dripped 
through  into  refining  vessels  placed  underneath. 

The  arc  furnace,  invented  by  Albert  A.  Shade,  is  specially 
adapted  to  the  fusion  of  silica  or  its  compounds,  as  in  glass 
manufacture,  but  is  also  applicable  to  other  electric  furnace 
processes.  The  hearth  is  a  long  inclined  trough,  of  circular 

170 


THEIR    INDUSTRIAL    APPLICATIONS 

section,  lined  with  refractory  material,  and  provided,  at 
its  upper  extremity,  with  a  screw  conveyor  or  other  device, 
for  securing  a  continuous  feed,  and  at  its  lower  end  with  a 
discharge  orifice  and  pouring  lip. 

The  diameter  of  the  lower  half  of  the  trough-shaped 
hearth  is  less  than  that  of  the  upper,  being  proportional 
to  the  desired  rate  of  passage  of  the  material  under  treatment, 
and  the  arc  electrodes,  arranged  in  diametrically  opposed 
pairs,  enter  through  the  side  walls  at  a  point  just  above 
the  reduced  diameter.  They  are  disposed  in  the  lower 
half  of  the  inclined  hearth  or  chute,  the  last  pair  of  elec- 
trodes being  very  near  the  discharge  opening.  In  line  with 
the  electrodes,  but  at  a  higher  elevation,  are  a  series  of 
pipes,  opening  into  the  furnace  chamber,  and  suitably 
protected  from  the  heat.  These  convey  exhaust  furnace 
gases  into  the  interior,  where  they  are  burnt,  and  serve  to 
dry  and  pre-heat  the  charge  during  its  descent,  thus  pre- 
paring it  for  the  more  advanced  heating  effect  of  the  arcs. 

Vertically  disposed  within,  and  entirely  surrounded  and 
protected  by  the  masonry  of  the  furnace  structure,  are  a 
series  of  electro-magnets,  one  to  each  pair  of  electrodes, 
with  its  active  poles  immediately  below  the  arcing  space. 
Sandwiched  between  each  neighbouring  pair  of  magnets 
is  an  iron  shield  plate,  also  embedded  in  the  masonry,  and 
serving  to  confine  the  effect  of  each  particular  magnet  to 
its  own  arc.  The  general  tendency  of  the  magnets,  when 
active,  is  to  deflect  the  arcs  downward  on  to  the  gradually 
moving  charge,  thereby  securing  an  enhanced  heating 
effect. 

A  flue  leads  from  the  top  of  the  furnace  chamber  to  a 
jacket  surrounding  the  conveyor  cylinder,  which  is  thus, 
with  its  contents,  also  subjected  to  a  preliminary  drying 
process,  the  jacketing  being  even  extended  to  the  hopper 
itself. 

Although  of  somewhat  complex  construction,  this  furnace 
would  certainly  appear  to  be  designed  with  a  view  to  taking 

171 


ELECTRIC    FURNACES    AND 

the  fullest  advantage  of  the  otherwise  waste  heat  of  the 
furnace  gases,  and  its  general  disposition,  in  addition  to 
being  well  thought  out,  indicates  that  the  inventor  is  fully 
alive  to  the  economies  attendant  on  an  efficient  system  of 
pre-heating  the  raw  materials,  and  reducing  the  duties  of 
the  electrical  portion  of  the  apparatus  to  a  minimum. 

The  Henrivaux  furnace  for  the  electrical  manufacture 
of  glass  comprises  three  steps  or  terraces,  composed  of  a 
refractory  material.  Immediately  over  the  surface  of 
each  step  is  disposed  a  powerful  arc,  and  the  raw  material, 
fed  from  a  hopper  into  the  heat  zone  of  the  topmost  arc, 
is  fused,  and  flows  down,  passing  in  turn  through  each  of 
the  two  remaining  arcs,  and  finally  reaching  a  receiver, 
or  trough,  into  which  it  drips. 

The  process  is  far  from  efficient  in  that  a  considerable 
quantity  of  the  heat  generated  is  dissipated  without  doing 
any  useful  work. 

Modern  gas-fired  glass  furnaces  call  for  a  consumption 
of  1-5  to  2-8  kgs.  of  coal  for  every  kilogramme  of  glass 
produced,  whereas  the  current  consumption,  in  the  Henri- 
vaux furnace,  for  a  similar  result,  is  equivalent  to  9-3  kgs. 
of  coal.  A  considerable  improvement  in  the  efficiency 
of  the  process  is,  however,  predicted. 

In  F.  A.  Becker's  electric  furnace  method  of  glass  manu- 
facture, the  raw  materials  are  passed  between  three  pairs  of 
carbon  electrodes.  The  first  two  pairs  serve  to  fuse  the 
materials,  with  an  expenditure  of  100  amperes  at  40  volts. 
The  third  pair  of  carbons  is  located  below  the  other  two 
and  maintains  the  fusion,  with  an  energy  expenditure  of 
50  amperes  at  40  volts.  Alternating  currents  are  used,  and 
the  process  is  continuous. 

Among  the  most  successful  of  electric  glass  furnace 
methods,  may  be  mentioned  the  Voelker  process,  which 
has  been  exploited  on  a  commercial  scale  at  Plettenberg, 
Westphalia. 

The  furnace  invented  by  August  Voelker  is  represented 

172 


THEIR    INDUSTRIAL    APPLICATIONS 


in  Fig.  41,  and  is  a  combination  of  the  arc  and  resistance 
types,  the  upper  portion  A  being  utilized  as  an  arc  furnace 
for  melting  the  raw 
materials ;  the  inter- 
mediate B  as  a  resist- 
ance furnace  for  a  species 
of  refining  process  which 
the  molten  mass  subse- 
quently undergoes  be- 
fore it  finally  overflows 
into  the  lower  receptacle 
or  trough  C. 

The  arc  furnace  A  is 
constructed,  as  usual,  of 
refractory  material,  and 
has  a  dome  d,  which 
reflects  the  heat  of  the 
arc  set  up  between  the 
two  electrodes  e  e  on 


to     the     raw     material, 

which  is    fed    by  screw  FlG-  41- 

conveyors  s   s  from  the 

hoppers  h   k,  and  delivered,  as  shown,  just    beneath    the 

electrodes. 

The  mass,  having  been  fused  by  the  reflected  heat  of  the 
arc,  flows  down  the  central  opening  or  chimney  c  into  the 
intermediate  resistance  furnace  B,  which  is  subdivided 
by  the  vertical  perforated  partitions  p  p  into  one  central, 
and  two  outer,  chambers.  In  these  latter  are  placed  the 
two  electrodes  /  /  of  the  resistance  furnace,  the  circuit 
between  them  being  completed  by  the  molten  glass.  The 
object  of  the  partitions  is  to  prevent  contamination  of  the 
fluid  mass  by  particles  which  might  become  detached 
from  /  /. 

In  this  intermediate  chamber  the  glass  becomes  more 
fluid,  and  the  bubbles  of  air  and  gas  carried  over  by  it  from 

173 


ELECTRIC    FURNACES    AND 

the  first  fusion  in  A  are  driven  off.  It  then  overflows 
into  the  cavity  C,  whence  it  is  drawn  off  as  pure  glass,  and 
is  ready  for  use  as  such. 

In  a  modified  form  of  the  Voelker  glass  furnace  construc- 
tion the  arcs  for  the  preliminary  fusion  of  the  raw  materials 
are  disposed  in  radial  channels,  converging  to  the  inter- 
mediate refining  chamber,  their  heated  gases  being  burnt 
below  the  final  reservoir,  where  they  assist  in  maintaining 
the  fluidity  of  the  molten  product. 

The  Bronn  process  for  the  manufacture  of  glass  in  the 
electric  furnace  has  been  devised  with  a  view  to  overcoming 
several  of  the  drawbacks  incidental  to  a  continuous  process, 
chief  among  which  may  be  mentioned  the  splitting  up  of 
the  charge,  whilst  passing  through  the  furnace,  into  unequal 
masses,  and  a  consequent  lack  of  homogeneity  in  the  manu- 
factured product  ;  contamination  of  the  molten  glass  by 
particles  detached  from  the  electrodes,  etc. 

In  the  Bronn  furnace,  invented  by  J.  Bronn,  of  Cologne, 
these  drawbacks  are  avoided.  Its  general  principles  of 
construction  and  operation  are  represented  in  Fig.  42, 
where  H  is  a  hopper,  in  which  the  raw  material  in  the  form 
of  a  powder  is  mixed  with  a  suitable  binding  substance, 
such  as  water-glass,  hydraulic  lime,  or  plaster,  which  will 
not  affect  the  transparency  or  purity  of  the  resultant 
glass. 

Having  undergone  the  process  of  mixing,  it  is  fed  down 
the  chute  C  to  the  rollers  R  R,  between  which  it  passes, 
and  is  thereby  transformed  into  a  continuous  and  homo- 
geneous sheet,  or  rod,  as  the  case  may  be,  the  particles 
being  held  together  by  the  water-glass  or  lime  before  men- 
tioned. 

It  next  passes  over  a  heated  roll  r,  which  drives  off  all 
moisture,  and  finally  emerges  on  to  the  upper  extremity  of 
an  inclined  plane  p,  forming  the  hearth  or  floor  of  the 
furnace.  Down  this  it  travels  at  a  regular  rate,  dependent 
upon  the  speed  of  fusion,  and  consequent  glass  formation, 

174 


THEIR    INDUSTRIAL    APPLICATIONS 

passing,  for  that  purpose,  under  the  arcs  playing  between 
the  electrodes  E'  E,  or,  if  in  rod  form,  travelling  down  the 
hearth  in  like  manner  between  opposite  pairs  of  arc  elec- 
trodes. 

A  comparatively  recent  patent  granted  to  J.  C.  T.  Kess- 


FIG.  42. 

meier  relates  to  the  application  of  an  electric  furnace  method 
as  an  auxiliary  in  the  casting  of  glass  articles.  The  extreme 
fluidity  required  for  the  successful  casting  of  molten  glass 
is  brought  about  by  arranging  a  pair  of  carbon  electrodes, 
through  which  a  current  is  caused  to  pass,  in  the  walls 
of  the  outlet  channel  from  the  ordinary  melting  crucible 
to  the  moulds. 

Having  first  been  reduced  to  a  molten  condition  in  the 
crucible  by  external  heat  in  the  ordinary  manner,  the  glass 
is  then  run  off  through  this  channel,  and,  in  passing  between 
the  two  electrodes,  completes  the  circuit  and,  by  virtue 
of  its  conducting  properties,  carries  sufficient  current  to 
raise  it  to  a  temperature  of  1,924°C.=3,500°F.,  or  even 
higher,  at  which  stage  it  becomes  extremely  fluid. 

No  mention  is  made  of  electrolytic  effects  produced  upon 
the  glass  by  the  current  in  passing,  though  it  seems  prob- 
able that  such  would  occur  with  a  uni-directional  current. 

175 


ELECTRIC    FURNACES    AND 


SECTION   VIII 

ELECTROLYTIC  FURNACES  AND   PROCESSES 

Aluminium. — Monkton,  as  early  as  1862,  was  granted 
an  English  patent  covering  the  reduction  of  alumina  by 
carbon  with  the  aid  of  electric  heat. 

Moissan  has,  however,  shown,  in  the  course  of  his  re- 
searches, that  such  a  process  is  commercially  impracticable, 
in  that  alumina,  even  when  in  a  liquid  or  molten  state,  is 
not  reducible  by  carbon,  it  being  necessary  to  vaporize 
both  substances,  and,  moreover,  heat  their  mixed  vapours 
to  a  very  high  degree  before  reduction  is  effected  ;  even 
then  the  product  is  partly  aluminium  carbide. 

Aluminium  was  first  prepared  by  Wohler  in  1828,  by 
heating  aluminium  chloride  in  the  presence  of  sodium.  The 
only  commercial  process  for  its  extraction,  prior  to  the 
introduction  of  the  thermo-electrolytic  method,  was  that 
of  heating  the  double  chloride  of  aluminium  and  sodium 
(2NaCl,  A12C16),  or  the  native  double  fluoride  (cryolite), 
with  sodium. 

One  of  the  earliest  instances  of  the  manufacture  of  alumi- 
nium by  electrolytic  methods  was  that  of  Lacassagne  and 
Thier's  primary  battery,  in  which  the  metal  was  produced 
as  a  by-product  of  the  battery  reaction. 

The  latter  consisted  of  an  outer  crucible,  heated  by  an 
ordinary  furnace  and  containing  chloride  of  sodium,  in 
which  was  immersed  an  iron  electrode.  In  this  was  placed 
a  porous  pot  containing  a  carbon  electrode  immersed  in 
chloride  of  aluminium.  The  furnace  served  to  bring  both 
salts  to  a  condition  of  fusion,  when  a  current  was  available 


THEIR    INDUSTRIAL   APPLICATIONS 

at  the  electrode  terminals,  and,  as  before  stated,  aluminium 
was  produced  as  a  by-product. 

The  price  of  aluminium  in  1855  was  approximately 
£56  per  kg.,  as  against  its  present  market  price  of  2s.  Id. 
per  kg.,  a  reduction  which  has  been  mainly  brought  about 
by  the  inception  of  the  electrolytic  processes  for  its  ex- 
traction from  alumina. 

Aluminium  is  one  of  the  most  abundant  metals  in  nature, 
constituting  from  ten  to  twenty  per  cent,  of  all  varieties 
of  clay,  in  the  form  of  silicates.  No  method  has,  up  to  the 
present,  been  forthcoming  for  the  economical  reduction  of 
aluminium  silicates,  and  the  metallurgist  has  consequently 
to  fall  back  upon  bauxite,  a  hydrated  alumina,  which  is 
found  in  France,  Ireland,  and  the  United  States  ;  and 
cryolite,  the  native  double  fluoride  of  aluminium  and  sodium, 
which  has  the  formula,  6NaP.Al2F6.  The  principal 
source  is  Arksut  Fiord,  West  Greenland.  These  two  sub- 
stances are  at  present  the  most  suitable  raw  materials  for 
the  production  or  separation  of  metallic  aluminium. 

Modern  progress  in  aluminium  manufacture  has  indicated 
the  desirability  of  dispensing  with  a  carbon  cathode,  and 
employing  the  molten  metal  itself  in  its  stead.  The  yield 
is  about  1  kilogramme  per  14  k.w.  hours,  the  power  being 
only  a  small  item  in  the  total  cost  of  manufacture. 

The  principal  expense  is  entailed  in  the  preparation  of 
the  pure  alumina  from  crude  bauxite,  a  process  which 
accounts  for  fully  40  per  cent,  of  the  total  cost  of  manu- 
facture. Crude  bauxite  contains  iron,  silicon,  titanium, 
and  several  other  undesirable  impurities. 

The  heat  of  formation  of  A1203  is  392,600  Calories; 
therefore,  according  to  Thomson's  rule,  a  minimum  E.M.F. 
of  2-8  volts  is  required  at  the  terminals  of  the  aluminium 
furnace  in  order  to  bring  about  the  separation  of  the  metal 
from  its  compound,  alumina.  This  voltage,  multiplied 
by  the  number  of  coulombs  passed  through  the  furnace, 
represents  the  electrical  energy  which  is,  during  the  reaction, 

177  N 


ELECTRIC    FURNACES    AND 

converted  into  chemical  energy,  and  stored,  as  such,  in  the 
metallic  aluminium.  It  may,  when  desired,  be  converted 
into  heat  energy  by  causing  the  aluminium  to  again  enter 
into  combination  with  oxygen,  as,  for  example,  in  the 
"  Thermite  "  process. 

The  electrical  reduction  of  aluminium  from  alumina  was 
first  effected  at  Cleveland,  Ohio,  U.S.A.,  the  site  of  the 
Cowles  Electric  Smelting  and  Aluminium  Co.  The  Cowles 
syndicate  was  organized  in  1886,  at  Stoke-on-Trent,  where 
electric  smelting  works  were  erected.  It  was  re-organized 
in  1894  as  the  British  Aluminium  Company,  with  works  at 
the  Falls  of  Foyers,  in  Scotland. 

Electrolytic  processes  for  the  manufacture  of  aluminium 
were  patented  during  the  period  1886-1887,  by  Hall  in 
America,  and  Heroult  in  England  and  France.  It  was 
worked  on  a  commercial  scale  at  Pittsburg  by  Hall  as 
early  as  1888. 

According  to  Roberts-Austen,  the  cost  of  purified  alumina, 
as  manufactured  from  bauxite,  constitutes  45  per  cent, 
of  the  total  cost  of  aluminium  manufacture.  Crude 
bauxite  often  contains,  in  addition  to  alumina,  oxides  of 
iron,  silicon,  and  titanium. 

One  of  the  disadvantages  of  the  Bayer  process  (described 
further  on)  for  extracting  alumina  from  bauxite,  lies  in 
the  presence  of  sodium  carbonate,  one  of  the  auxiliary 
compounds  necessary  to  bring  about  the  initial  fusion. 
Once  mixed  with  this  compound,  it  is  almost  impossible 
to  entirely  eradicate  it  from  the  otherwise  purified  alumina. 

Hall's  process  for  the  extraction  of  pure  alumina  from 
bauxite,  patented  in  1901,  has  led  to  the  production  of  a 
grade  of  alumina,  very  different,  both  in  appearance  and 
characteristics,  to  that  resulting  from  Bayer's  method. 

In  the  specifications  relating  to  Hall's  patents  for  the 
purification  of  bauxite,  two  processes  are  dealt  with.  The 
bauxite  to  be  treated  is  represented  as  having  the  following 
composition — 


THEIR   INDUSTRIAL  APPLICATIONS 


Alumina 
Ferric  oxide 
Silica 

Titanic  oxide 
Water 


60  per  cent. 

18     „        „ 
2-3     „ 
3-4 


17     „ 

The  first  method  consists,  briefly,  in  calcining  the  bauxite, 
after  which,  from  eight  to  ten  per  cent,  of  carbon  is  added, 
and  the  mixture  fused  in  a  carbon-lined  electric  furnace, 
with  carbon  electrodes.  The  fusion  is  maintained  for  about 
an  hour,  the  current  being  either  alternating  or  continuous. 
The  outcome  of  thus  heating  the  molten  mass  in  the  pre- 
sence of  carbon,  is  that  the  impurities  are  reduced,  and  sink 
to  the  hearth  of  the  furnace  in  the  form  of  an  alloy. 

If  the  percentage  of  iron  present  as  an  impurity  be  low, 
or  the  other  impurities,  silica  and  titanic  oxide,  corre- 
spondingly high,  it  is  an  advantage  to  add  more  iron  to  the 
fused  mass,  either  as  oxide,  or  in  the  metallic  state,  to  aid 
the  separation. 

The  second  method  is  practically  identical,  in  principle, 
with  the  first,  the  only  difference  being  the  substitution 
of  metallic  aluminium  for  carbon  as  the  reducing  agent. 
As  before,  a  preliminary  analysis  of  the  bauxite  is  made, 
and  sufficient  aluminium  added  to  combine  with  the  whole 
of  the  oxygen  known  to  be  present  as  a  constituent  of  the 
various  impurities.  The  mass  is  then  subjected  to  fusion 
in  the  electric  furnace  for  about  one  and  a  half  hours,  during 
which  the  latter  separate  out,  as  in  the  previous  case,  but 
without  evolution  of  gas.  The  same  procedure,  in  the 
event  of  a  low  iron  content,  should  be  adopted  here,  as 
in  the  first  case,  and  the  iron  may  conveniently  be  associated 
with  the  added  aluminium  in  the  form  of  a  powdered  alloy 
containing  about  50  per  cent,  of  each  metal. 

The  theoretical  output  of  aluminium  at  maximum 
efficiency  is  2-85  kgs.  per  1  k.w.  per  24  hours.  In  actual 
practice,  however,  the  efficiency  of  the  process  is  very  low, 
and  '6  kg.  of  aluminium  per  k.w.  day  is  probably  nearer 
the  mark. 

179 


ELECTRIC   FURNACES    AND 

About  2  kgs.  of  anhydrous  alumina  are  required  for 
the  manufacture  of  1  kg.  of  metallic  aluminium,  from  which 
it  will  be  seen  that  the  cost  of  the  raw  material  is  no  in- 
considerable item  in  the  total  cost  of  manufacture.  The 
consumption  of  carbon  electrodes  is  also  a  source  of  expense, 
the  theoretical  figure,  66  per  cent,  of  the  weight  of  alu- 
minium manufactured,  usually  increasing,  in  practice,  to 
100  per  cent.,  or  weight  for  weight  with  the  metallic  product. 

The  following  are  two  estimates  of  the  cost  of  aluminium 
manufacture,  the  latter  being  based  on  the  Hall  process — 


PER  KILOGRAMME 
OF  ALUMINIUM. 

Power       .          .          ,          .          ,          *          .          .  '  4-8cZ. 

Alumina    .           .          .          .....          .  8-8d. 

Carbon  electrodes       .           .          .                     .          T  4-4d. 

Labour,  superintendence,  interest  on,  and  repairs 

to  furnaces           ......  4-4d. 


Total  .          .        ..          .  .  22-4d. 

Power       .          .          .  ....  .  4-6d. 

Alumina    .          »          .  ,          .          .          .  .  13-9rf. 

Carbon  electrodes       .  .       •  .          .          .  .  3-5d. 

Miscellaneous  1  •  3d. 


Total 23-3d. 

There  is  one  important  point  in  connexion  with  the 
electrolytic  manufacture  of  aluminium,  and  that  is  the 
necessity  for  maintaining  that  difference  between  the 
specific  gravities  of  the  liberated  metal,  and  the  fused 
electrolyte,  which  will  ensure  their  occupying  correct  rela- 
tive positions  in  the  furnace,  or,  in  other  words,  to  keep 
the  aluminium  at  the  bottom. 

The  following  table,  published  by  Richards,  shows  the 
specific  gravities  of  the  various  substances  employed  in 
aluminium  manufacture,  in  both  a  fused  and  solid  state, 
and  it  will  be  seen  that  the  margin  of  weight,  causing  the 
liberated  aluminium  to  remain  at  the  bottom,  is  not  great. 

180 


THEIR    INDUSTRIAL    APPLICATIONS 

SPECIFIC  GRAVITIES. 
FUSED.  SOLID. 

Commercial  aluminium       .          .          .      2-54  .      .      2-66 

Commercial  Greenland  cryolite  .          .      2-08  .      .      2-92 

Cryolite  saturated  with  alumina   .  .      2-35  .      .      2-90 

Cryolite  mixed  with  aluminium  fluoride 
in  the  proportion  indicated  by  the 

formula  Al2F6-2NaF    .          .          .      1-&7  .      .      2-96 
The  above  saturated  with  alumina              2-14  2-98 


In  the  Zeitschrift  fur  Elektrochemie,  January  2  and  9, 
1902,  were  published  some  details  of  laboratory  experiments, 
carried  out  by  Messrs.  Haber  &  Geipert  in  regard  to  the 
electrolytic  production  of  aluminium. 

The  object  of  the  experiments  was  to  determine  the  actual 
E.M.F.,  current  density,  etc.,  necessary  to  bring  about  the 
reaction.  They  were  carried  out  in  the  laboratory  of  the 
Technical  College  at  Karlsruhe,  the  apparatus  employed 
being  a  small  carbon  crucible,  with  a  central  carbon  anode 
arranged  axially  therein.  In  this  furnace  the  authors  suc- 
ceeded in  obtaining  metallic  aluminium  from  an  electrolyte, 
consisting  of  a  mixture  of  two-thirds  aluminium  and  sodium 
fluorides,  and  one-third  alumina,  the  current  employed 
being  from  300  to  400  amperes  at  7  to  10  volts,  representing 
a  current  density  of  3  amperes  per  square  centimetre. 

The  central  anode  was  gradually  raised  as  the  operation 
proceeded,  whilst  the  high  percentage  of  aluminium  fluoride 
present  rendered  the  bath  very  fluid. 

The  resultant  metal  contained  only  0-05  per  cent,  carbon 
and  0-034  per  cent,  silicon,  and  had  a  tensile  strength  of 
from  13-7  to  17-3  kgs.  per  square  millimetre. 

In  1903,  there  were,  according  to  Kershaw  (Electrical 
Review,  March  20,  1903),  nine  factories  engaged  in  the  pro- 
duction of  aluminium,  either  by  the  Hall  or  Heroult  process ; 
they  are  located  as  follows  :  America,  3  ;  United  Kingdom, 
1  ;  France,  2  ;  Germany,  1  ;  Switzerland,  1  ;  Austria,  1. 

The  aggregate  power  available  at  these  several  factories 
is  between  36,000  and  40,000  H.P.,  all  derived  from  water. 

181 


ELECTRIC    FURNACES    AND 

A  reliable   estimate  places  the  output  for  1901  and  1902 
of  the  : 

1901  1902 

Six  European  works,  at      .          .      4,000  tons       .       .      3,800    tons 
Three  American  works,  at  .      3,240     „          .       .      4,200     „ 


Totals        .          .      7,240     „          .       .      8,000     „ 

In  November,  1902,  the  prices  of  the  Pittsburg  Reduction 
Company  were  as  follows  — 


No.   1  Metal,  guaranteed  over  99  per  cent.  16^d.  to  18^d.  per  Ib. 

„      2     „                  „                  „    90     „     „  15id.    „      lid.  „      „ 
Nickel-aluminium  alloy  (less  than  10  per 

cent,  nickel)           ....  16|d.    „    19|d.  „      „ 

Powdered  aluminium             .           .          ,  45(7.    ,,      50d.  ,,      ,, 

Aluminium  castings      .          .                     .  22|d.  ,,      ,, 

All  the  above  prices  were  subject  to  discounts  ranging 
from  10  to  15  per  cent.,  whilst  European  competition  is 
stifled  by  an  import  duty  of  4d.  per  Ib.  on  ingot  metal,  and 
.  per  Ib.  on  sheet. 

American  prices  for  aluminium  rod  and  wire,  ranged  from 
.  to  26d.  per  Ib.,  according  to  gauge,  a  rebate  of  l\d.  to  2d. 
being  allowed  off  list  price,  according  to  the  magnitude  of 
the  order. 

The  (1903)  prices  of  the  British  Aluminium  Company  were 
as  follows  — 

Ingot    metal    (guaranteed    over 

99  per  cent,  aluminium)    .      Ifi^d.  per  Ib.  less  7^  per  cent. 
Ingot  metal  (98  to  99  per  cent.)15rf.        „      „      „     7|     „     „ 
„      (No.  4  alloy)          16d.        „      „      „     2|     „      „ 
„      (No.  6  alloy)     .      13fd. 
Wolframinium  alloy       .  .      17M 

Aluminium   wire,    Nos.    1-14 
S.W.G.  .       ...         , 


The  American  output  of  aluminium  is  controlled  by  the 
Pittsburg  Reduction  Company,  with  two  factories  at  Niagara 
Falls,  and  one  at  Shawinigan  Falls. 

The  European  manufacturers  are  the  Aluminium  Industrie 
Aktien-Gesellschaft,  with  works  at  Neuhausen,  Rheinfelden, 
and  Lend  Gastien  ;  the  Societe  Electrometallurgique  Fran- 

182 


THEIR    INDUSTRIAL    APPLICATIONS 

9aise,  with  works  at  Froges  and  La  Praz  ;  and  the  Compagnie 
des  Produits  Chimiques  d'Alais,  with  works  at  St.  Michel, 
France.  The  only  British  concern  engaged  in  the  industry 
is  the  British  Aluminium  Company,  with  works  at  Foyers, 
N.B. 

The  United  States,  represented  by  the  Pittsburg  Reduction 
Company,  who  control  the  whole  of  the  patents  therein,  is, 
of  course,  the  principal  producer.  It  has  in  operation  at 
Niagara  Falls,  plant  utilizing  some  11,000  H.P.,  and  at 
Shawinigan  Falls,  Quebec,  operating  under  the  title  of  the 
Royal  Aluminium  Company,  5,000  H.P.,  the  two  works  being 
capable  of  manufacturing  4,500  tons  of  aluminium  per 
annum.  In  addition,  the  former  Company  has  lately  pur- 
chased a  site  at  Massena,  New  York,  where  it  is  installing 
a  plant  of  12,000  H.P. 

The  British  Aluminium  Company  employs  the  Heroult 
process,  and  has  an  available  plant  of  14,000  H.P.  The 
Heroult  process  is  also  exploited  by  the  Societe  electro- 
metallurgique  Fran9aise,  at  La  Praz.  The  Compagnie  des 
Produits  Chimiques  d'Alais,  at  St.  Michel,  employ  the  Hall 
and  Minet  process,  whilst  the  Aluminium  Industrie  Aktien- 
Gesellschaft,  with  an  aggregate  of  14,000  H.P.,  also  utilises 
the  Heroult  process. 

The  following  table  represents  the  production  of  alumin- 
ium in  the  United  States,  from  1883  to  1902,  inclusive. 


YEAR. 

POUNDS.      YEAR. 

POUNDS. 

1883 

83       1893 

333,629 

1884 

'  150       1894 

550,000 

1885 

-283       1895 

920,000 

1886 

3,000       1896 

1,300,000 

1887 

18,000       1897 

4,000,000 

1888 

19,000       1898 

5,200,000 

1889 

47,468       1899 

6,500,000 

1890 

61,281       1900 

7,150,000 

1891 

150,000       1901 

7,150,000 

1892 

250,885       1902 

7,300,000 

The  Heroult  Process. — In  the  Heroult  process  of  aluminium 
manufacture,  the  lining  of  the  furnace  hearth  is  protected 

183 


ELECTRIC    FURNACES    AND 

from  electro-chemical  action  by  a  layer  of  cooled,  solidified 
electrolyte. 

The  voltage  theoretically  required  to  bring  about  the 
electrolysis  of  the  alumina  in  the  Heroult  process,  is  2-2. 
Very  good  quality  carbon  is  required  for  the  anodes,  which 
are,  of  course,  consumed  in  the  process,  and,  if  at  all  impure, 
would  tend  to  contaminate  the  resultant  metal. 

The  bauxite  used  in  the  manufacture  of  aluminium  by  the 
Heroult  process  at  Foyers,  is  obtained  from  Larne,  in  Ireland, 
and,  according  to  Blount,  has  the  following  percentage  com- 
position— 

56  per  rent. 


Alumina 
Ferric  oxide 
Silica 

Titanic  acid 
Water 


3 

12 
3 

26 


100 


The  method  of  preparing  alumina  from  this,  being  an 
essential  part  of  the  Heroult  process  of  aluminium  manu- 
facture, a  brief  description,  extracted  from  Practical 
Electro-Chemistry,  by  Bertram  Blount,  is  included. 

"  The  material  is  crushed  so  as  to  pass  a  quarter-inch 
mesh  sieve,  and  is  gently  roasted  in  a  revolving  calcining 
furnace,  the  temperature  being  regulated  so  as  to  destroy 
any  organic  matter,  and  ensure  that  all  iron  shall  be  present 
as  Fe203,  and  nevertheless  not  to  render  the  alumina  in- 
soluble. The  roasted  material  is  powdered  so  as  to  pass  a 
sieve  having  thirty  meshes  per  linear  inch,  and  is  digested 
with  a  solution  of  caustic  soda  of  specific  gravity  1-45  at  a 
pressure  of  70  to  100  Ibs.  per  square  inch.  After  digestion 
for  two  or  three  hours,  the  solution  is  diluted  to  a  specific 
gravity  of  1-23,  and  is  passed  through  filter  presses,  and 
afterwards  through  cellulose  filters,  consisting  of  sieves 
carrying  a  layer  of  cellulose  pulp,  the  whole  contrivance 
somewhat  resembling  the  laboratory  apparatus  known  as  a 
Gooch  crucible.  3y  this  double  filtration  a  satisfactory, 

184 


THEIR    INDUSTRIAL    APPLICATIONS 

clear  liquor  is  obtained.  In  former  processes  for  the  manu- 
facture of  alumina,  the  alkaline  aluminate  was  decomposed 
with  C02,  and  the  alumina  was  thus  precipitated.  The  dis- 
advantage of  this  process,  apart  from  the  cost  of  the  C02, 
is,  that  any  silica  present  in  solution  is  also  thrown 
down  and  contaminates  the  alumina,  and,  moreover,  the 
alkali  is  converted  into  carbonate,  and  has  to  be  recausticised 
before  it  can  be  used  again  for  extraction.  By  Bayer's  pro- 
cess, which  is  that  now  in  use,  the  caustic  solution  of  alumina 
is  treated  with  a  small  portion  of  alumina,  precipitated  in  a 
previous  operation  ;  it  is  thereby  caused  to  deposit  about 
70  per  cent,  of  its  dissolved  alumina,  if  the  solution  is  well 
agitated  and  the  precipitation  allowed  to  continue  for  about 
36  hours.  The  clear  liquor  is  drawn  off,  and  the  alumina 
washed  in  a  filter  press,  and  dried  to  some  extent  by  a  blast 
of  air,  being  then  roasted  at  about  1,100°C.  =  2,012°F.,  in 
order  to  render  it  both  anhydrous  and  non-hygroscopic. 
The  latter  quality  is  necessary,  as  otherwise  the  alumina 
would  absorb  water  during  storage,  and  would  not  be  fit  to 
feed  into  the  electrolytic  cell. 

"  The  caustic  soda  solution,  diluted  by  retaining  a 
portion  of  its  alumina,  is  concentrated  in  a  triple  effect 
vacuum  evaporator,  to  its  original  specific  gravity  of  1-45, 
and  is  then  ready  for  the  extraction  of  another  portion  of 
bauxite.  It  will  be  seen  that  the  caustic  soda  serves  merely 
to  pick  out  the  alumina  from  its  accompanying  impurities, 
and  to  deposit  it,  as  it  were  at  the  word  of  command,  in  a 
pure  state." 

The  Heroult  furnace  in  use  at  Foyers  consists  of  a  square 
iron  casing  A,  Fig.  43,  lined  with  carbon  C,  and  containing 
the  cathode  F,  which,  in  the  form  of  a  cast-iron  plate,  rests 
on  the  bottom  -of  the  furnace,  and  is  connected  externally 
with  the  source  of  current.  The  anode  consists  of  a  bundle, 
or  fagot  of  carbon  rods  B  suspended  over  the  furnace 
cavity  and  adjustable  as  to  its  height  and  consequent  depth 
pf  immersion  therein. 

185 


ELECTRIC    FURNACES    AND 


The  furnace  is  first  filled  with  cryolite,  which  is  speedily 
fused  when  the  current  is  switched  on,  after  which  powdered 

alumina  is  fed  in  at  a 
regular  rate.  The  differ- 
ence of  potential  between 
the  furnace  terminals  is 
from  3  to  5  volts,  the 
metallic  aluminium  col- 
lecting at  the  negative 
electrode,  whilst  oxygen 
_  gas  is  set  free  at  the  posi- 
tive, or  carbon  electrode, 
with  which  it  enters  into 
combination,  forming  the 
gases  monoxide  and  di- 
oxide of  carbon.  The 
Current  density  is  1'9 
amperes  per  square  centi- 
metre of  cathode  surface,  amounting  to  about  8,000 
amperes  per  furnace,  and  the  temperature  at  which  the 
operation  is  carried  out  varies  from  750°  to  850°C.=  1,382° 
to  1,562°F. 

The  electrolyte  employed  in  the  Heroult  process  consists  of 
a  mixture  of — 


FIG.  43. 


Fluoride  of  calcium 

Double  fluoride  of  aluminium  and 

sodium  (cryolite) 
Fluoride  of  aluminium    . 


234  parts  by  weight. 

421     „       „         „ 

845 


From  3  to  4  per  cent,  of  a  suitable  chloride,  that  of  calcium, 
for  example,  is  added,  together  with  sufficient  alumina  to 
form  a  very  stiff  mixture. 

The  Hall  Process. — The  distinguishing  features  between  the 
Heroult  and  Hall  processes  may  be  regarded  as  almost 
entirely  of  a  mechanical  nature,  including  the  method  of 
operation,  and  such  minor  details  incidental  thereto  as  are 
essential  to  the  efficiency  of  the  process. 

186 


THEIR    INDUSTRIAL    APPLICATIONS 

Mr.  Chas.  M.  Hall,  the  originator  of  the  aluminium  pro- 
cess now  exploited  by  the  Pittsburg  Reduction  Company, 
first  experimented  with  his  process  at  the  works  of  the 
Cowles  Electric  Smelting  and  Aluminium  Company,  Lock- 
port,  New  York,  U.S.A. 

The  furnace  hearths  are  of  cast  iron,  lined  interiorly  to 
some  considerable  thickness  with  carbon  ;  they  are  6  ft. 
long  by  3  wide  by  10  in.  deep,  and  constitute  the  cathode. 
The  anodes  consist  of  a  number  of  carbon  rods,  mounted  in  a 
special  holder,  and  immersed,  at  their  lower  extremities, 
in  the  molten  electrolyte.  Each  individual  unit  of  the 
anode  carries  a  current  of  250  amperes,  and  the  total  current 
required  for  the  operation  is  in  the  neighbourhood  of  10,000 
amperes. 

The  E.M.F.  is  5  volts,  the  power  consumed  being  approxi- 
mately 65  H.P.  The  furnaces  are  worked  in  series. 

The  process  consists  in  the  electrolysis  of  purified  alumina, 
dissolved  in  a  molten  bath  of  the  double  fluoride  of  alumin- 
ium and  sodium  (A12  F6.2NaF).  The  inventor  has  pub- 
lished the  following  data  relating  to  the  cost  of  the  materials 
for  the  process  of  aluminium  manufacture  patented  by  him — 

Alumina  .          *          .  2|d.  to  3d.  per  pound. 

Cryolite     .          .          ...  3d. 

Hydrofluoric  acid       .          .          .  2d.  to  2%d.     „         ,, 

Carbon  for  lining  furnace  hearths  l|d.  „  2d.       ,,         ,, 

The  electrolyte  used  in  the  Hall  process  is  prepared  in  a 
lead-lined  vat,  by  treating  a  mixture  of  alumina,  cryolite, 
and  fluorspar  with  hydrofluoric  acid  ;  the  mass  is  then  dried 
and  placed  in  the  furnaces,  where  it  is  subjected  for  some 
time  to  the  heating  action  of  the  current,  in  order  to  reduce 
it  to  a  state  of  complete  fluidity  before  the  alumina  is  fed  in. 

The  proportions  most  commonly  used  are — 

Aluminium  fluoride        .          .          .,677  parts  by  weight. 
Sodium  ,,  ...      251      ,,  „ 

Calcium  „  .          .          .234      „ 

When  fusion  has  been  completely  effected,  pure  alumina 


ELECTRIC    FURNACES    AND 

is  fed  in,  in  the  proportion  of  20  per  cent,  by  weight  of  the 
solvent,  and  the  like  proportion  maintained  as  the  operation 
proceeds.  The  temperature  at  which  the  Hall  furnace 
operates  is  below  982°C.=1,800°F. 

The  Pittsburg  furnaces  are  tapped  once  a  day,  the  removal 
of  the  molten  metal  being  accompanied  by  a  corresponding 
increase  in  the  electrical  resistance  of  the  furnace  charge. 
Visual  indication  of  the  increased  resistance  is  obtained  by 
means  of  an  ordinary  incandescent  lamp,  which  is  connected 
in  shunt  between  the  electrodes,  and,  by  its  increased 
brilliancy,  indicates  that  the  resistance  of  the  fused  elec- 
trolyte is  rising  and  that  fresh  alumina  must  be  fed  in. 

The  following  rules,  to  be  observed  in  the  thermo-elec- 
trolytic  manufacture  of  aluminium,  have  been  formulated 
and  published  by  Mr.  Hunt,  President  of  the  Pittsburg 
Reduction  Company. 

(1)  The  solvent,   with   its   dissolved    alumina,   must    be 
fusible  at  a  moderate  temperature. 

(2)  The  solvent  must  dissolve  alumina  freely,  e.g.,  must 
take  up  at  least  20  per  cent,  at  the  working  temperature. 

(3)  The  critical  voltage  for  the  solvent  must  be  higher 
than  that  for  the  alumina. 

(4)  The  specific  gravity  of  the  solvent  at  its  working 
temperature  must  be  lower  than  that  of    the  aluminium 
at  the  same  temperature,  so  that  the  metal  may  collect  at 
the  bottom  of  the  cell. 

Extended  litigation  has  resulted  in  the  Cowles  and  Bradley 
patent  claims  in  the  manufacturing  process,  being  upheld 
in  the  United  States  Courts,  with  the  result  that  the  Pitts- 
burg Reduction  Company  is  now  reported  to  be  under  a 
working  agreement  with  the  owners  of  ^  these  patents  as  to 
royalties,  etc. 

Theoretical  Considerations. — M.  Gustav  Gin  contributed  a 
theoretical  paper  on  the  subject  of  aluminium  manufacture 
at  the  Fifth  International  Congress  of  Applied  Chemistry, 
the  salient  features  of  which  mav  be  summarised  as  follows — 

188 


THEIR    INDUSTRIAL   APPLICATIONS 

According  to  Minet,  the  physical  conditions  of  the  fused 
electrolyte  employed  should  be  — 

(1)  Low  fusion  point. 

(2)  Sufficient  fluidity  during  the  process  to  permit  the 
molten  aluminium  to  separate  out. 

(3)  Fusion  density  to  be  lower  than  that  of  aluminium. 

(4)  Low  vapour  tension,  and  low  ohmic  resistance. 
From  a  chemical  point  of  view,  and  for  a  minimum  ex- 

penditure of  energy,  the  aluminium  compound  selected  for 
electrolysis  should  have  a  low  heat  formation  value.  The 
E.M.F.  required  for  the  electrolysis  of  fused  aluminium 
compounds  may  be  divided  under  two  headings,  viz.  — 

(1)  That   necessary   to   overcome    the   ohmic   resistance 
of  the  fused  electrolyte,  and  the  polarisation  of  the  elect- 
rodes, and  secure  the  required  current  density,  and  — 

(2)  That   required  to   effect   the   electrolysis   and  bring 
about  the  discharge  of  the  ions. 

The  first  is  easily  obtainable,  whilst  the  second  is  a  func- 
tion of  the  heat  of  formation,  and  can  also  be  arrived  at 
by  calculation.  Minet  has  proved  experimentally  that, 
at  the  temperature  of  the  molten  mass  in  the  aluminium 
extraction  process,  aluminium  fluoride  is  completely  dis- 
sociated into  its  constituent  elements.  The  following 
thermal  equation  therefore  applies  — 

Q=jF+JA1* 

=50,750  +  40,100  C.  gr.  d. 
=90,850  C.  gr.  d. 

from  which,  since  23,0670.  gr.  d.  are  equivalent  to  one  volt, 
we  get  E=3-93  volts. 

Assuming  the  fluorine  thus  liberated  enters  into  com- 
bination with  carbon  at  the  anode  to  form  carbon-tetra- 
fluoride  (CFJ,  the  equation  then  becomes  — 


=  (50,750  +  40,100)  -33,400 
=  57,450  C.  gr.  d. 
189 


ELECTRIC   FURNACES   AND 

from  which,  E— 2-49  volts,  a  value  more  nearly  in  agree- 
ment with  that  obtained  experimentally  by  Minet  (2-5 
volts). 

Passing  on  to  a  consideration  of  the  electrolysis  of  alumina, 
we  have 

Q  =  Jo*  +  JAI*    -J(CO*) 
=:  (34,950  +  40, 100)  -24,400 
=  50,650  C.  gr.  d. 
and  E=2-19  volts. 

The  above  calculations  have  been  experimentally  con- 
firmed by  Gin,  who  obtained  the  figure,  2-30  volts,  as  the 
mean  of  four  observations  in  Le  Blanc's  method  of  deter- 
mining potential  differences. 

The  thermal  equation  for  aluminium  sulphide  is  : 

Q=Js*  +  J**    -J   (C*   S*) 
=(-6,300  +  40,100)  -4,350 
=29,450  C.  gr.  d. 
or  E  =  l-27  volt. 

From  these  data  we  arrive  at  the  energy  required  to  pro- 
duce one  kilogramme  of  aluminium  from  any  of  the  three 
compounds  mentioned.  They  are  as  follows — 

Al2F6=Kr  +  8-5  K.W.  Hours 
Al203=Ko  +  7-5      „ 

Al2S3=Ks+4-4      „ 

where  KF,  Ko,  and  Ks  are  quantities  varying  between  16 
and  19  k.w. 

The  difference  in  the  energy  required  by  any  of  these 
three  compounds  does  not  therefore  exceed  5  k.w.  hours 
per  kg.  of  aluminium  produced,  and  M.  Gin  therefore  con- 
cludes that  any  future  improvement  in  the  economy  of 
aluminium  manufacture  will  depend  upon  the  cost  of  the 
raw  materials,  and  not  upon  a  corresponding  improvement 
in  the  efficiency  of  the  process  itself. 

Chlorine  Smelting  with  Electrolysis. — The  Swinburne- 

190 


THEIR    INDUSTRIAL    APPLICATIONS 

Ashcroft  or  "  Phoenix  "  process  of  so-called  chlorine  smelt- 
ing, which  is  the  joint  invention  of  Mr.  Jas.  Swinburne, 
M.I.G.E.,  and  Mr.  E.  A.  Ashcroft,  is  a  cyclic  process  for 
obtaining  various  metals  from  their  ores,  which  can  be  con- 
ducted with  little  or  no  loss,  and  has,  therefore,  a  promising 
future  in  competition  with  the  present  wasteful  methods 
of  smelting  by  reduction  processes. 

It  is  appropriately  called  "  chlorine  smelting,"  because 
chlorine  is  the  vehicle  employed  to  displace  the  sulphur 
from  the  sulphide  ores  under  treatment,  only  to  be  re- 
covered by  a  subsequent  stage  in  the  process,  and  used  over 
again. 

Various  papers  and  articles  dealing  with  the  process  have 
been  published  from  time  to  time,  including  a  recent  one 
by  Mr.  Swinburne  himself,  read  before  the  Faraday  Society 
on  June  30,  1903,  which  deals  mainly  with  the  financial 
aspect  of  the  process. 

The  principal  features  are  as  follows  :  The  process  con- 
sists in  three  main  stages,  which  are  thus  rendered  by  Mr. 
Swinburne  in  the  form  of  chemical  equations.  Employing 
the  usual  chemical  symbols  for  zinc,  chlorine,  and  sulphur, 
and  substituting  M  and  N  for  other  metals  present  in  mixed 
sulphide  ores,  Stage  I.  is  represented  by  the  equation — 

ZnS  +MS  +NS  +  3C12  =  ZnCl2  +MC12  +NC12  +  3S. 
Stage  II.,  after  the  removal  of  the  sulphur,  by — 
ZnCl2  +  MC12  +  NC12  +  2Zn = 3ZnCl2  +  M  +  N 

and,  finally,  Stage  III.,  consisting  in  electrolysis  of  the  zinc 
chloride — 

3ZnCla=3Zn  +  3Cl2 

To  put  it  briefly  into  words,  the  process  consists  in  first 
treating  the  sulphide  ores  with  chlorine,  which  displaces 
the  sulphur,  and  itself  enters  into  combination  with  the 
metals  thus  set  free  to  form  chlorides,  which  latter  are 
then  subjected  to  electrolysis,  whereby  the  metal  is  sepa- 

191 


ELECTRIC   FURNACES    AND 

rated  out,   and  the  chlorine  recovered,   to   be  used  over 
again. 

Take  galena  as  an  example.  It  may  or  may  not  contain 
silver,  and  even  gold.  It  is  first  treated  with  chlorine  in 
the  presence  of  heat,  which  leads  to  the  formation  of  lead 
chloride  and  sulphur,  the  latter  being  thrown  down  or 
condensed  in  the  form  of  brimstone,  whilst  the  former,  if 
it  be  known  to  contain  admixtures  of  the  precious  metals, 
is  again  treated  with  metallic  lead,  which  replaces  them. 
The  precious  metals,  if  present,  form  an  alloy  with  the 
excess  of  metallic  lead  present,  producing  a  metallic  mix- 
ture of  any  desired  richness,  limited  only  by  its  melting  point. 

With  the  exception  of  a  slight  loss,  which  arises  in  prac- 
tice, out  of  the  leakage  of  air  into  the  vats,  forming  sulphur 
dioxide,  the  sulphur  is  also  saved. 

The  process  is  precisely  similar  with  other  ores,  or  mix- 
tures of  ores,  and  is  especially  applicable  to  such  refractory 
samples  as  have  hitherto  presented  untold  difficulties  to 
the  metallurgist. 

Though  consisting  partly  in  a  thermo-chemical,  and 
partly  in  an  electrolytic  process,  or  combination  of  processes, 
and  therefore  not  coming,  in  its  entirety,  strictly  under  the 
category  of  electrolytic  furnace  methods,  it  will  be  neces- 
sary to  treat  of  the  process  in  full,  in  order  to  render  it 
clear  to  the  reader. 

The  crude  ores  are  first  crushed,  and  then  fed  into  a  re- 
ceptacle, called  for  convenience  a  transformer,  and  resem- 
bling in  general  appearance  a  small  blast  furnace.  It  is 
constructed  of  iron,  and  lined  with  fire-clay.  Like  a  blast 
furnace,  it  has  a  small  cone  at  the  top,  whilst  an  opening 
at  the  base,  fitted  with  a  carbon  tube,  serves  for  the  intro- 
duction of  the  chlorine.  Outside  the  transformer,  con- 
nexion is  made  between  this  tube  and  an  iron  pipe,  which 
conveys  the  chlorine  to  it.  The  action  of  the  apparatus 
is  continuous,  and  we  will  assume  that  it  is  partly  filled 
with  fused  chlorides,  and  gangue  floating  on  top. 

192 


THEIR    INDUSTRIAL    APPLICATIONS 

Fresh  ore  is  fed  in  at  the  top,  and,  simultaneously,  chlorine 
is  pumped  in  at  the  base  by  way  of  the  iron  pipe  and  car- 
bon tube.  It  bubbles  up  through  the  fused  mass,  and  in 
its  passage  combines  with  the  metals  present  to  form  chlo- 
rides, liberating  the  sulphur,  which  passes  off  as  a  vapour, 
and  is  suitably  condensed. 

This  chemical  action  produces  a  great  deal  of  heat, 
which  serves  to  maintain  the  contents  of  the  apparatus  at 
the  necessary  fusion  temperature,  and  thus  render  it  self- 
heating.  The  temperature  regulation  is  an  important 
point ;  if  it  be  too  low,  chloride  of  sulphur  is  formed,  while, 
on  the  other  hand,  if  it  be  too  high,  some  of  the  chlorides 
distil  over,  and  are  condensed  with  the  sulphur.  It 
is  regulated  within  the  limits  of  practice,  which  allows 
a  fairly  wide  margin,  by  controlling  the  rate  of  admission 
of  the  chlorine.  The  size  of  the  transformer  is  also  a  con- 
trolling feature,  and  must  be  such  that,  when  running  at 
full  load,  sufficient  heat  is  driven  off  by  conduction,  and 
radiation  from  the  outer  surface,  to  keep  the  contents  at 
or  about  the  required  temperature. 

In  treating  Broken  Hill  slimes,  which  have  already  been 
tried,  for  purposes  of  experiment,  by  Messrs.  Swinburne 
and  Ashcroft,  a  transformer,  having  a  capacity  of  10  tons, 
was  successfully  employed,  but  Mr.  Swinburne  ventures 
the  opinion  that  a  larger  size,  with  thinner  lining,  would 
probably  yield  improved  results. 

Visual  indication  as  to  the  state  of  the  transformer  con- 
tents during  the  progress  of  the  operation,  and  whether  a 
further  supply  of  ore  is  required,  may  be  secured  by  making 
a  hole  at  the  top  of  the  transformer.  The  sulphur  vapour 
and  gaseous  products  in  passing  over  through  the  legitimate 
outlet  to  the  condensers  and  chimney  create  a  slight  indraft 
of  air  at  this  opening,  with  the  result  that  sulphur  dioxide 
is  formed,  and  burns  with  a  blue  name.  This  latter  indi- 
cates that  all  is  well,  and  that  sufficient  ore  is  present.  If 
there  be  an  insufficiency  of  ore  in  the  transformer,  fumes 

193  o 


ELECTRIC  FURNACES   AND 

of  ferric  chloride  are  formed  at  the  top  of  the  chamber,  and 
pass  over  with  the  sulphur  vapour  ;  it  is  necessary  to  avoid 
this  contingency,  and  the  ore  feed  must  consequently  be 
watched  until  the  process  is  completed. 

When  the  transformer  is  full,  the  supply  of  ore  is  stopped, 
but  the  process  is  continued  until  brown  fumes  begin  to 
make  their  appearance.  The  charge  is  then  tapped  off, 
and  permitted  to  cool. 

The  intermediate  or  chemical  stage  of  the  process  varies 
with  the  ores  under  treatment,  depending  naturally  upon 
the  metals  present.  It  is  best  described  in  Mr.  Swinburne's 
own  words,  the  Broken  Hill  slimes  being  again  taken  as  an 
example. 

"  We  now  come  to  the  intermediate  or  chemical  stage 
of  the  process.  This  varies  with  the  ore  used.  We  may 
take  the  Broken  Hill  slimes,  and  imagine  there  is  copper 
too.  This  would  be  about  as  troublesome  an  ore  as  we 
could  have.  We  have  used  the  Broken  Hill  ore,  and  mixed 
it  with  a  Tasmanian  copper  ore,  but  we  have  chiefly  worked 
on  it  alone.  The  fused  mass  from  the  transformer  con- 
sists of  chlorides  of  lead,  zinc,  iron,  manganese,  copper, 
silver  and  gangue.  It  is  run  into  water,  and  through  a 
filter  press  when  cool  enough.  This  takes  out  the  gangue 
and  lead  chloride,  carrying  most  of  the  silver.  The  gangue 
is  easily  separated  from  the  lead  and  silver  chlorides,  and 
these  chlorides  are  then  dried  and  fused  in  contact  with 
lead,  which  extracts  the  silver  and  any  gold  ;  and  then 
with  zinc,  which  gives  lead,  practically  pure,  and  anhy- 
drous neutral  zinc  chloride,  which  is  ready  for  the  electro- 
lysis vats. 

"  The  filtrate  from  the  press  contains  a  little  lead  and 
silver,  in  solution,  and  copper,  iron,  manganese,  and  zinc. 
The  lead  and  silver  are  taken  out  with  spongy  copper. 
The  copper  is  taken  out  as  sponge  or  '  cement '  by  zinc, 
and  we  have  left  iron,  manganese  and  zinc  chlorides. 

"  The  iron  is  chlorinated  up  to  the  ferric  state,  and  zinc 

194 


THEIR  INDUSTRIAL  APPLICATIONS 

oxide  is  added  to  cause  precipitation.  This  throws  down 
hydrated  ferric  oxide.  This  is  the  base  of  iron  paint,  and 
is  marketable,  its  value  depending  on  the  colour  obtained. 
The  solution  is  further  chlorinised  in  the  presence  of 
more  zinc  oxide,  and  the  manganese  goes  down  as  per- 
oxide. 

"  We  have  now  substituted  zinc  for  all  the  other  metals 
in  their  chlorides,  and  have  nothing  left  but  zinc  chloride. 
This  is  evaporated  down  carefully,  and  fused.  This  de- 
composes some  of  the  chloride,  and  makes  an  oxy chloride. 
Steinhart  evaporates  in  vacuo,  to  produce  neutral  anhydrous 
zinc  chloride.  We  have  not  done  this  ;  we  find  that  with 
cautious  boiling  down  there  is  not  much  oxygen  in  the 
final  result. 

"  This  is  got  rid  of  in  open  preliminary  vats,  which  use 
inexpensive  anodes,  which  are  gradually  used  up.  The 
consumption  is  less  than  if  all  the  oxygen  went  off  as  mon- 
oxide. The  anhydrous  neutral  chloride  from  these  vats  is 
then  added  to  that  from  the  lead  chloride  substitution, 
and  is  taken  to  the  final  electrolysis  vats." 

The  final  stage,  which  constitutes  the  part  actually  played 
by  the  electrolytic  furnace,  has  for  its  object,  as  before 
stated,  the  final  separation  of  the  remaining  metal  (zinc), 
and  the  recovery  of  the  chlorine. 

The  furnace  itself  is  a  very  simple  affair,  consisting  of  an 
iron  chamber,  lined  with  fire-brick  ;  in  course  of  time  the 
fused  chloride  permeates  the  pores  of  this  lining,  and  solidi- 
fies therein,  so  that,  in  reality,  the  lining  itself  ultimately 
becomes  one  of  chloride. 

The  cathode  is  of  fused  zinc,  and  the  anode  of  carbon, 
which  latter  is  not  attacked  by  chlorine.  Some  care  is 
necessary  in  the  selection  of  a  suitable  grade  of  carbon, 
but,  once  found,  the  anodes  stand  extremely  well,  and  are 
permanent,  the  temperature  not  being  sufficiently  high  to 
cause  combustion. 

In  practice,  a  slight  suction  is  kept  on  the  furnace  during 

195 


ELECTRIC    FURNACES    AND 


the  electrolysis,  so  that,  if  there  be  any  leakage,  it  is  in  the 
nature  of  ingress  of  air  rather  than  egress  of  chlorine. 

In  the  experiments  which  have  been  conducted  up  to 
the  present,  a  comparatively  small  furnace,  consuming 
3,000  amperes,  has  been  used  ;  but  a  10,000  ampere  furnace 
is  being  tried,  this  being  the  maximum  current  density 
which  can  conveniently  be  dealt  with.  An  electromotive 
force  of  approximately  4  volts  per  furnace  is  necessary  to 
maintain  the  action. 

The  furnace  used  in  the  experimental  trials  of  the  process, 
carried  out  at  the  old  Cowles  Aluminium  works  at  Milton, 

Staffordshire,  is  illus- 
trated in  section  in 
Fig.  44.  It  consists 
of  an  outer  steel  shell 
S,  6  ft.  in  diameter, 
lined  for  a  depth  of 
18  in.  with  fire-brick, 
the  inner  layers  be- 
ing  set  in  a  special 
cement.  The  brick- 
work B  forms  a 
cylindrical  chamber 

or  hearth  H,  at  the  bottom  of  which  is  placed  the 
cathode  Z,  in  the  shape  of  a  mass  of  molten  zinc,  weighing 
approximately  one  ton.  Electrical  connexion  with  this 
latter  is  secured  by  means  of  a  massive  steel  block  A  let 
into  a  recess  in  the  brickwork,  and  connected  with  the 
external  circuit  by  fire  screwed  copper  tubes  t  t,  which  are 
also  made  part  of  a  system  through  which  air  is  caused  to 
circulate  for  cooling  purposes.  F  is  the  anode,  and  con- 
sists of  an  iron  cover  plate  grouted  in  place  with  a  special 
heat-resisting  cement,  and  serving  as  a  terminal  support 
for  120  2  J-inch  hard  carbon  rods  c  c,  which  are  submerged 
in  the  molten  electrolyte  to  a  depth  of  about  six  inches. 
The  current  required  to  operate  a  furnace  of  this  descrip- 

196 


THEIR    INDUSTRIAL    APPLICATIONS 

tion  is  from  3,000  to  4,000  amperes  at  4  to  4-5  volts,  the 
working  temperature  being  475°C=  887°F.,  and  the  out- 
put one  ton  of  metallic  zinc  per  week. 

The  cost  of  working  the  process  is,  roughly,  30<s.  per  ton 
of  ore,  plus  the  cost  of  the  electrical  energy. 

Sodium  and  Caustic  Soda. — Dr.  Rogers,  as  early  as  1889, 
studied  the  possibilities  of  preparing  lead-sodium  alloys  by 
electrical  means,  and  actually  succeeded  in  manufacturing 
an  alloy  containing  17  per  cent,  of  sodium,  by  the  electro- 
lysis of  fused  sodium  chloride  in  a  30  Ib.  crucible.  A  lead 
cathode  was  employed,  and  the  process  called  for  an  ex- 
penditure of  72  amperes  at  21  volts  for  a  period  of  2 
hours. 

To  this  investigator  belongs  the  credit  of  having  first 
suggested  a  basic  lining  for  the  furnace  used  in  the  electro- 
lysis of  fused  sodium  chloride. 

Dr.  Borchers's  process  of  sodium  extraction  by  deposi- 
tion of  the  metal  upon  a  flowing  stream  of  lead  involved  a 
current  density  of  3-2  amperes  per  square  inch  of  cathode, 
the  E.M.F.  being  6  to  8  volts. 

C.  T.  J.  Vautin's  process  was  originally  based  upon  an 
attempt  to  obtain  caustic  solutions  and  chlorine,  but,  owing 
to  certain  natural  and  unforeseen  tendencies  on  the  part 
of  the  various  constituents  of  the  electrodes  and  electro- 
lyte, the  system,  when  tried  at  Keighley,  Yorkshire,  in 
1893  to  1894,  proved  commercially  impracticable. 

Vautin,  however,  suggested  the  maintenance  of  fusion 
of  the  electrolyte  by  electric  heat,  and  both  this  suggestion, 
and  that  of  Dr.  Rogers  concerning  basic  linings  for  the 
furnaces,  constitute  two  at  least  of  the  essential  features 
of  Acker's  successful  solution  of  the  problem. 

The  Vautin  process  consisted  in  the  electrolysis  of  fused 
sodium  chloride,  employing  a  lead  cathode,  which  was 
intended  to  alloy  with  the  sodium  at  the  moment  of  libera- 
tion, and  thus  protect  it  from  further  action,  electrolytic 
or  otherwise. 

197 


ELECTRIC    FURNACES    AND 

The  practical  difficulties  which  led  to  the  abandonment 
of  the  process  were  the  destruction  of  the  containing  vessel 
by  the  combined  action  of  the  contents  at  high  tempera- 
tures, and  the  failure  of  the  cathode  surface  to  remain 
active  once  the  action  had  been  started,  owing  to  the  forma- 
tion of  a  crust  of  the  lead-sodium  alloy,  which  impeded 
further  combination  between  the  two  metals  ;  the  sodium 
subsequently  set  free  either  burning  away  on  rising  to  the 
surface  of  the  fused  electrolyte,  or  re-combining  with  the 
nascent  chlorine  to  form  sub-chlorides. 

Leon  Hulin,  in  1890,  commenced  experimenting  at  Modane, 
France,  independently  of  Vautin,  and  without  knowledge 
of  what  had  already  been  accomplished  in  the  igneous 
electrolysis  of  sodium  chloride.  In  order  to  get  over  the 
crust  formation  difficulty,  which  led  to  the  failure  of  Vautin's 
process,  a  compound  electrolyte  was  employed,  contain- 
ing a  definite  proportion  of  lead  chloride.  Electrolysis 
resulted  in  the  simultaneous  liberation  of  lead  and  sodium 
at  the  cathode,  which  immediately  combined  to  form  the 
alloy,  and,  in  this  condition,  were  immune  from  the  action 
of  the  chlorine  set  free  at  the  anode. 

The  electrolyte  consisted  of  the  mixed  chlorides  of  lead 
and  sodium,  whilst  the  anodes  were  also  compound,  con- 
sisting of  carbon  and  lead,  the  latter,  or  metallic  portion, 
being  connected  in  circuit  with  a  controlling  resistance  or 
rheostat,  by  means  of  which  the  proportion  of  the  main 
current  passing  through  it  could  be  controlled,  and  the 
amount  of  lead  dissolved  and  deposited  similarly  governed. 

The  Hulin  process  has  been  worked  on  a  limited  indus- 
trial scale  at  the  paper  works  of  MM.  Matussiere  et  Forest, 
Modane.  Four  furnaces  were  employed,  the  terminal 
E.M.F.  of  each  being  7  volts,  and  the  current  density 
between  1-5  and  2-5  amperes  per  square  centimetre  of 
cathode  surface.  The  best  results  were  obtained  with  a 
current  density  of  1-9  amperes  per  square  centimetre.  A 
composite  lead-carbon  anode  was  used,  the  metallic  portion 

198 


THEIR    INDUSTRIAL    APPLICATIONS 


only  conveying  a  fraction  (12  per  cent.)  of  the  total  cur- 
rent, and  by  its  combination  with  the  chlorine  liberated 
serving  to  maintain  the  requisite  proportion  of  lead  chlo- 
ride in  the  electrolyte.  The  yield  per  k.w.  hour  is  said  to 
have  been  108  grammes  chlorine,  and  72  grammes  sodium, 
or  2-48  kgs.  chlorine,  and  1-66  kgs.  sodium  per  k.w.  day 
of  23  hours. 

According  to  Kershaw,  the  theoretical  voltage  required 
in  the  process 
is  4-2,  and  the 
yield,  per  k.w. 
hour,  356 
grammes  of 
caustic  soda  and 
314  grammes 
of  chlorine. 
Against  these 
may  be  set  the 
actual  figures 
obtained  in1 
practice,  viz.,  7, 
150,  and  129, 

respectively,  showing  a  current  efficiency  of  69-3,  and  an 
energy  efficiency  of  41-5  per  cent. 

The  Acker  electrolytic  furnace,  for  the  manufacture  of 
caustic  soda  from  fused  electrolytes,  as  exploited  by  the 
Acker  Process  Company  at  Niagara  Falls,  is  shown  in 
diagrammatic  section  in  Fig.  45.  It  consists,  essentially, 
of  a  rectangular  trough-like  structure  or  hearth  F,  having 
a  steel  base  s,  refractory  side  walls  m  of  magnesia,  and  a 
removable  horizontal  false  bottom,  or  dividing  partition  p, 
also  of  steel.  A  flue  /  provides  for  the  escape  of  the  chlo- 
rine gas  evolved  during  the  process,  which  may  be  used 
for  the  manufacture  of  bleaching  powder,  whilst  one  end 
of  the  structure  slopes  to  a  well  W  fitted  with  an  injector  A, 
for  the  introduction  of  steam  under  pressure.  The  catho- 

199 


ELECTRIC    FURNACES    AND 

die  or  negative  electrode  connexion  with  the  source  of 
current  is  made  through  a  metal  tube  T  communicating 
with  the  well  W.  The  anodes  C  C  are  cylindrical  graphite 
rods,  projecting  vertically  through  the  cover  to  within  a 
short  distance  of  the  steel  partition  p.  N  is  a  mass  of  the 
raw  material,  sodium  chloride  or  common  salt,  which  is 
packed  on  top  of  the  furnace,  and  performs  a  triple  duty, 
viz.,  that  of  conserving  the  heat  generated,  hermetically 
sealing  all  except  the  legitimate  gas  outlets,  and  providing 
a  source  of  supply  as  the  charge  becomes  exhausted.  P  is 
a  mass  of  molten  lead,  extending  upwards  to  a  level  slightly 
above  that  of  the  false  bottom,  or  partition  p,  and  in  elec- 
trical connexion  with  the  cathode. 

The  process  of  operation  is  as  follows  :  Steam  being 
admitted  to  the  injector  through  the  inlet  pipe  i,  carries 
up  with  it,  from  the  base  of  the  injector  well,  a  mixture  of 
lead,  caustic  soda,  and  hydrogen  gas,  the  resultant  products 
of[the  electrolytic  process  going  on  in  F.  On  reaching  the 
upper  chamber  above  the  well,  W,  these  three  constituents 
part  company,  the  alloy  flowing  back,  over  an  inclined  par- 
tition, into  the  main  furnace  F,  whilst  the  caustic  liquid 
passes  over  into  the  receiver  R.  Hydrogen  gas  is  available 
at  the  outlet  o,  and  may  be  utilized  for  a  variety  of  purposes, 
chief  among  which  may  be  mentioned  its  application  to 
an  oxyhydrogen  burner  or  burners  for  the  preliminary 
fusion  of  the  charge. 

The  following  facts,  in  connexion  with  the  Acker  process, 
as  carried  on  at  Niagara  Falls,  were  published  by  the  in- 
ventor in  the  course  of  a  paper  read  by  him  before  the 
American  Electro-Chemical  Society  at  Philadelphia,  in  1902. 
Each  furnace  has  four  anodes,  and  consumes  a  total  current 
of  8,000  amperes  or  2,000  amperes  to  each  anode,  represent- 
ing a  current  density  of  3  amperes  per  square  centimetre. 

The  efficiency  of  the  process  is  100  per  cent.,  and  the 
works  have  been  in  continuous  operation  since  1900,  with 
but  few  temporary  accidental  interruptions. 

20Q 


THEIR    INDUSTRIAL    APPLICATIONS 

The  only  trouble  experienced  is  said  to  have  been  in  the 
electrode  connexions  at  the  carbon-copper  junction,  the 
metal  being  gradually  corroded  or  eaten  away.  An  im- 
proved method  of  construction  has,  however,  minimised 
this  drawback. 

The  anodes  consist  of  graphitised  carbon  blocks,  and  are 
manufactured  by  the  International  Acheson  Graphite  Com- 
pany. There  are  four  to  each  furnace,  each  block  having 
a  section  approximately  7J  by  14  inches,  and  carrying 
2,000  amperes.  They  are  unattacked  by  the  electrolyte, 
the  only  weak  point  being  the  junction  between  the  metal 
terminal  clamps  and  the  carbon.  This  is  protected  by  a 
sleeve  of  basic  cement. 

The  furnaces  are  lined  with  magnesite  bricks,  placed 
loosely  in  position,  without  cement,  but  held  together  firmly 
by  the  solidified  electrolyte,  which  permeates  them  when  in 
a  fused  condition,  and,  on  solidifying,  locks  them  rigidly 
together. 

In  1902  Acker  furnaces  to  the  number  of  forty-five  were 
in  operation,  consuming  3,250  E.H.P.,  or  8,000  amperes 
at  300  volts.  Each  individual  furnace  requires  a  current 
of  8,000  amperes  at  7  volts  terminal  E.M.F.,  or  75  E.H.P.,  and 
produces,  on  an  average,  290  kgs.  of  anhydrous  caustic  daily. 

The  successful  conduct  of  the  process  consists  in  con- 
tinuously removing  the  sodium  alloy  as  quickly  as  it  forms, 
the  reason  being  that  it  is  unstable  in  the  presence  of  the 
fused  salt. 

The  steam  from  the  injector  performs  a  double  office, 
in  that  it  sets  up  a  rapid  circulation,  and  also  oxidises  the 
sodium  of  the  alloy  formed,  producing  fused,  anhydrous, 
sodium  hydrate  (NaOH). 

The  chlorine  gas  evolved  during  the  process  is  drawn  off 
by  means  of  a  fan,  and  utilized  in  the  manufacture  of  bleach- 
ing powder.  The  furnaces  are  of  cast  iron,  lined  to  a  level 
above  that  of  the  fused  lead  ;  they  are  arranged  in  pairs, 
one  on  either  side  of  a  common  flue. 

201 


ELECTRIC    FURNACES    AND 

The  Elliott-Cresson  Medal  of  the  Franklin  Institute  has 
been  awarded  to  Mr.  Chas.  E.  Acker  for  his  electrolytic 
method  of  manufacturing  caustic  soda  and  chlorine  as 
described  above. 

The  advantages  of  the  Acker  process,  as  compared  with 
other  purely  electrolytic  methods,  are  thus  epitomised  by 
the  Committee  who  recommended  the  award — 

(1)  Its  directness. 

(2)  The  very  heavy  current  sent  through  each  pot. 

(3)  The  absence  of  the  evaporation  of  caustic  and  boiling 
down  to  dryness. 

(4)  The   absence    of   water   solutions,    requiring   special 
pumps,  and  a  complicated  circulating  system. 

(5)  The  absence  of  mercury. 

The  disadvantages,  on  the  other  hand,  are — 

(1)  A  large  power  consumption,  6-75  volts,  in  place  of  4-5. 

(2)  The  rapid  destruction  of  the  apparatus. 

(3)  The  rapid  destruction  of  the  anodes. 

(4)  The  more  arduous  work  of  the  pot-men. 

Calculations  on  the  part  of  the  committee  show  the  fol- 
lowing distribution  of  the  total  energy  required,  throughout 
the  various  stages  of  the  process — 

54  per  cent,  is  usefully  applied  to  chemical  separation  of 
the  sodium  from  the  chlorine. 

9  per  cent,  in  fusing  the  salt. 

Lost  by  radiation,  37  per  cent. 

In  the  later  types  of  furnace  for  the  application  of  the 
Acker  process  of  caustic  soda  manufacture,  a  more  rapid 
circulation  of  the  fused  lead  is  secured  by  means  of  a  bladed 
propeller,  which  revolves  at  the  bottom  of  the  injector  well. 
The  effect  of  this  additional  feature  is  said  to  be  a  more  con- 
centrated product,  in  that  less  steam  is  required  than  was 
the  case  in  the  original  apparatus,  where  it  was  depended 
upon  to  produce  the  requisite  mechanical  agitation  of  the 
lead. 
[  Castner's  sodium  process  consists  in  the  electrolysis  of 


THEIR    INDUSTRIAL    APPLICATIONS 

fused  sodium  hydrate.  An  iron  pan,  or  crucible,  contains 
the  electrolyte,  which  is  initially  fused  by  a  furnace  below 
it.  The  cathode,  of  nickel,  passes  vertically  up  through  an 
opening  in  the  base,  and  is  surrounded,  at  its  upper  extre- 
mity, by  an  annular  anode,  also  of  nickel.  The  fused  con- 
dition of  the  electrolyte  is  partially  maintained  by  an 
excess  current,  and,  for  the  remainder,  by  the  auxiliary  com- 
bustion furnace.  Sodium  is  set  free,  in  liquid  form,  and 
rises  to  the  surface  of  the  molten  mass,  whence  it  is  periodi- 
cally removed. 

Temperature  regulation  needs  to  be  very  exact,  as,  if  the 
heating  effect  be  only  slightly  in  excess  of  that  required, 
recombination  of  the  liberated  sodium  takes  place,  and  no 
metal  is  set  free. 

The  current  efficiency  of  the  process  is  from  70  to  90  per 
cent.,  and  it  is  in  commercial  operation  at  Runcorn,  in 
this  country,  Niagara,  U.S.A.,  and  in  Germany  and  France. 

The  Niagara  plant  consists  of  some  120  furnaces,  each 
of  which  requires  a  current  of  1,200  amperes,  at  an  E.M.F. 
of  5  volts  to  operate  it. 

The  total  output  of  sodium  in  1897  was  260  tons. 

Commenting,  in  Zeitschrift  fur  Elektrochemie,  about  the 
beginning  of  1903,  on  the  Castner  process  for  the  extraction 
of  sodium,  Professor  Le  Blanc  and  Herr  Erode  remark  that 
neither  the  inventor  nor  those  associated  with  the  conduct 
of  the  process  on  an  industrial  scale  understand  exactly 
what  goes  on  in  the  furnace  during  the  reaction.  They 
therefore  conducted  experiments  with  a  view  to  ascertain- 
ing this,  and  summarise  their  results  as  follows — 

(1)  Molten  sodium  hydrate,  containing  water,  shows  two 
decomposition  values :   1-3,  and  2-2  volts.     When  water  is 
absent,  the  lower  of  these  two  values  disappears. 

(2)  At  the  lower  E.M.F. ,  hydrogen  and  oxygen  are  sepa- 
rated ;  at  the  higher   E.M.F.,   sodium  and  oxygen.     The 
yield  of  oxygen  is  never  quantitative,  but  it  increases  with 
the  current.     The  yield  of  hydrogen  is  quantitative  under 

203 


ELECTRIC    FURNACES    AND 

2-2  volts,  so  long  as  no  free  sodium  is  separated  at  the 
cathode.  When  no  water  is  present  in  the  hydrate  as  an 
impurity,  only  sodium  is  obtained,  with  an  E.M.F.  above 
2-2  volts.  This  fact  proves  that  pure  molten  sodium 
hydrate  contains  only  the  ions  Na  and  OH,  and  that 
neither  O  nor  H  ions  are  present  in  the  electrolyte. 

(3)  Molten   caustic   soda   quickly   arrives   at   a   state   of 
equilibrium  as  regards  moisture  exchanges  with  the  atmo- 
sphere.    Normally  it   contains   a   considerable   amount   of 
water  ;  if  it  contains  no  water,  it  is  strongly  hygroscopic. 

(4)  Molten  caustic  soda,   containing  free  sodium  as    an 
impurity,   yields   hydrogen  at   the   anode,   in   addition   to 
oxygen,  on  electrolysis  with  high  current  densities.     This 
evolution  of  hydrogen  can  only  result  from  the  separation 
and  discharge  of  OH  ions. 

The  same  authorities  are  responsible  for  the  statement 
that  potassium  cannot  be  similarly  separated  by  electro- 
lysis of  its  fused  hydrate,  as  claimed  in  the  Castner  patent, 
but  that  oxidation  has  to  be  guarded  against  by  depositing 
a  layer  of  petroleum  on  the  surface  of  the  fused  mass,  when 
globules  of  metallic  potassium  are  set  free. 

G.  P.  Scholl  has  improved  upon  the  original  method  by 
effecting  an  economy  in  the  current  required,  and,  at  the 
same  time,  eliminating  the  evolution  of  hydrogen,  which 
takes  place  at  the  cathode  in  Castner's  process.  He  adds  to 
the  fused  electrolyte  some  50  per  cent,  of  sodium  sulphide, 
and  reduces  the  voltage  of  the  operation  to  that  required 
for  the  decomposition  of  the  sulphide  only  ;  theoretically, 
1-8  volt.  Sodium  is,  as  before,  set  free  at  the  cathode, 
whilst  the  liberated  sulphur,  reacting  with  the  fused  caustic, 
again  forms  sulphide  of  sodium,  which  is  again  electrolysed, 
and  so  the  cycle  goes  on,  fresh  caustic  being  added  from 
time  to  time  in  quantities  proportional  to  the  sodium  set 
free.  The  process  is  said  to  effect  a  considerable  economy 
in  current,  as  compared  with  the  original  Castner  method. 

The  Fischer  process  for  the  electrolytic  manufacture  of 

204 


THEIR    INDUSTRIAL    APPLICATIONS 

sodium  is  represented  diagrammatically  in  Fig.  46,  where 
C,  is  a  shallow  crucible,  or  furnace  hearth,  divided  into  two 
portions  by  a  central  partition  p,  which  does  not  extend 
quite  to  the  bottom.  The  electrodes  E  E2  are  horizontally 
disposed,  being  introduced  through  the  walls  of  the  crucible. 
The  anode  E  is  a  carbon  rod,  whilst  the  cathode  E2  is  a 
metal  tube,  placed  with  its  axis  on  a  level  with  the  surface 
of  the  fused  electrolyte.  The  side  of  the  crucible  contain- 
ing the  negative  tubular  electrode  E2  is  kept  cool  by  a 
water  jacket,  not  shown  in  the  figure.  The  raw  charge 
consists  of  a  mix- 
ture of  79  parts  by 
weight  of  potassium 
chloride,  with  59  of 
sodium  chloride,  or 
common  salt.  The  ^ 

resultant  sodium  FiG.  46. 

contains  an  admix- 
ture  of  about  1   per  cent,  of  potassium,  and  is  drawn  off 
through  the  tubular  electrode  E2. 

The  Darling  electrolytic  furnace,  which  is  employed  in 
the  manufacture  of  nitric  acid  and  metallic  sodium  from 
nitrate  of  soda,  is  of  comparatively  simple  construction. 
The  anode  consists  of  an  outer  iron  vessel,  within  which 
are  placed  two  concentric  cylinders  of  perforated  iron.  A 
shunt  connexion  between  these  latter  and  the  outer  iron 
anode  protects  them  from  injury  during  the  action  of  the 
furnace,  whilst  the  space  between  the  two  perforated  walls 
is  filled  in  with  powdered  magnesia. 

The  fused  salt,  sodium  nitrate,  is  contained  within  the 
inner  of  the  two  cylinders,  the  cathode,  a  carbon  rod,  being 
immersed  in  it.  Nitric  acid  gas  is  set  free  in  the  outer 
space  between  the  walls  of  the  anode  and  the  concentric 
cylinders,  and  is  conveyed,  by  an  outlet  pipe,  to  condensing 
apparatus,  where  it  is  converted  into  the  liquid  acid.  The 
sodium,  on  the  other  hand,  rises  to  the  surface  of  the  fused 

205 


ELECTRIC   FURNACES   AND 

salt  contained  within  the  inner  perforated  cylinder,  whence 
it  is  removed  at  intervals  by  means  of  a  ladle,  and  placed 
in  tin  vessels  containing  a  small  quantity  of  paraffin,  which 
effectually  protects  it  from  the  action  of  the  atmosphere. 
The  fall  of  potential  between  the  terminals  of  each  furnace, 
whilst  the  operation  is  in  progress,  is  15  volts.  A  current 
of  400  amperes  per  furnace  is  required. 

The  Darling  process  is  worked  by  Harrison  Bros.  &  Co., 
of  Philadelphia. 

Calcium  and  Strontium. — Calcium,  as  is  well  known  to 
the  chemist  and  metallurgist,  is  of  great  value  in  various 
industries  as  a  reducing  agent,  the  only  drawback  to  its 
widespread  use  being  its  present  comparatively  high  market 
value,  which  renders  it  unsuitable  for  all  but  experimental 
purposes,  where  the  question  of  cost  is,  within  certain 
limits,  no  object. 

The  high  price  charged  for  the  metal  calcium  is  due  to 
the  expensive  method  of  production,  which  consists  in 
subjecting  a  dilute  solution  of  calcium  chloride  to  electro- 
lysis in  the  presence  of  a  mercury  cathode  ;  an  amalgam 
of  calcium  with  mercury  is  thus  obtained,  from  which  the 
mercury  is  subsequently  driven  off  by  the  aid  of  heat. 

Apart  from  the  cost  of  the  process,  pure  calcium  is  never 
produced  by  this  method,  there  being  always  a  small  per- 
centage of  metallic  mercury  present  in  the  resultant  product. 

Messrs.  Borchers  and  Stockem,  recognising  the  need  for 
a  cheaper  and  more  efficient  method  of  production,  turned 
their  attention  to  the  possibilities  offered  by  an  electric 
furnace  method,  and  have  recently  succeeded  in  designing 
an  electrolytic  furnace  in  which  pure  metallic  calcium  is 
readily  manufactured  from  its  fused  chloride. 

The  fundamental  principle  involved  consists  in  the 
employment  of  a  small  cathode,  and  correspondingly 
large  anode,  between  which  the  fused  mass  is  brought  to 
a  red  heat,  when  -the  metallic  calcium  makes  its  appearance 
around  the  former  as  a  spongy  mass.  On  removing  this 

206 


THEIR    INDUSTRIAL    APPLICATIONS 


latter  from  the  furnace,  and  immersing  it  in  petroleum,  a 
porous  residue  is  obtained,  some  50  to  60  per  cent,  of  which 
consists  of  pure  calcium.  The  mass  is  compressed  or 
squeezed  whilst  still  warm,  in  order  to  get  rid  of  the 
chloride  with  which  it  is  saturated,  and  a  product  containing 
fully  90  per  cent,  of  pure  metal  is  the  result.  The  latter 
is  then  fused  in  an  hermetically  sealed  chamber,  and  there- 
by converted  into  a  firm  silvery  mass  of  metallic  calcium. 
Calcium  is  claimed  to  have  been  produced  by  this  method  at 
a  cost  of  approximately  3<9.  per  kilogramme,  about  1/5, 000th 
of  the  cost  of  the  original  process. 

To  pass  on,  however,  to  a  consideration  of  the  furnace 
employed  ;  let  us  turn  our 
attention  to  Fig.  47,  which 
represents  a  section  of  the 
latter.  It  consists  of  an 
outer  carbon  cylinder  C 
built  up  of  several  longi- 
tudinal sections,  each 
keyed  into  its  neighbour, 
and  the  whole  held  to- 
gether by  a  metal  ring  or 
band  B,  which,  at  the 
same  time,  constitutes  a  FlG-  47- 

terminal    connexion,    the 
carbon  cylinder   being  the  anode. 

The  upper  portion  of  the  cylinder  is  open,  whilst  its  lower 
end  is  closed  by  a  fire-clay  cylinder  c  surrounding  and 
insulating  a  metal  chamber  A,  which  performs  the  double 
office  of  a  circulating  water  tank  for  cooling  purposes,  and 
a  support  for  the  cathode  Fe,  which  consists  of  an  iron  rod 
placed  axially  with  regard  to  the  cylindrical  anode,  and 
screwed  at  its  base  into  the  upper  portion  of  the  cooling 
chamber  A.  Inlet  and  outlet  pipes  i  and  o  respectively, 
serve  to  convey  the  water  to  and  from  the  chamber,  whilst 
it  is  protected  from  the  heat  of  the  furnace  by  a  layer  of 

207 


ELECTRIC    FURNACES    AND 

fluor-spar  s,  which,  owing  to  its  high  melting  point,  remains 
solid  during  the  operation  of  the  furnace. 

The  mass  of  calcium  chloride  M  is  placed  above  this,  the 
action  of  the  furnace  being  started  by  several  thin  carbon 
rods,  placed  radially,  like  the  spokes  of  a  wheel,  between 
the  iron  cathode  Fe  and  the  inner  surface  of  the  carbon 
cylinder.  The  heat  set  up  by  the  flow  of  current  through 
these  rods  serves  to  start  the  fusion  of  the  upper  layer  of 
chloride,  and  they  are  subsequently  removed,  leaving  the 
process  of  electrolysis  to  continue  through  the  initially 
fused  mass. 

The  position  taken  up  by  the  resultant  spongy  calcium 
is  indicated  in  the  figure  by  Ca. 

Strontium. — The  apparatus  for  the  manufacture  of 
strontium,  is,  with  some  slight  modifications,  incidental  to 
the  properties  of  the  separated  metal  itself,  similar  to  that 
detailed  above  for  the  production  of  calcium.  Unlike  the 
latter,  strontium  separates  out  from  its  compounds  in  the 
form  of  small  spherical  masses,  which  tend  to  rise  to  the 
surface  of  the  molten  salt,  and  there  again  enter  into 
chemical  combination  with  the  chlorine  from  which  they 
have  just  been  liberated. 

To  obviate  this  drawback,  the  iron  cathode  is  made 
shorter,  such  that  its  upper  extremity  only  reaches  to  a 
point  just  above  the  lower  edge  of  the  cylindrical  carbon 
anode.  The  latter  rests  upon  a  cylindrical  fireproof  struc- 
ture of  insulating  material,  such  as  fire-clay,  which,  in  turn, 
is  supported  in  a  cup-shaped  depression  in  the  upper  portion 
of  the  cooling  chamber.  The  latter  is,  in  the  strontium 
furnace,  given  a  larger  diameter  than  the  carbon  anode, 
and  it  is  in  the  central  depression  or  basin,  around  which 
the  anode  rests,  that  the  metallic  strontium  collects  during 
the  action  of  the  furnace,  and  is  solidified  by  the  cooling 
effect  of  the  circulating  water. 

The  temperature  of  the  operation  in  Borchers'  and 
Stockem's  electrolytic  manufacture  of  metallic  calcium,  is 

208 


THEIR    INDUSTRIAL   APPLICATIONS 

a  red  heat,  above  the  melting  point  of  calcium  chloride, 
but  below  that  of  metallic  calcium. 

Dr.  K.  Arndt,  commenting  on  the  former  method  for  the 
manufacture  of  metallic  calcium,  in  Zeitschrift  fur  Elektro- 
chemie,  November  13,  1902,  states  that  he  has  obtained 
a  similar  result  with  simpler  apparatus. 

His  furnace  consisted  of  a  coated  iron  crucible,  a  carbon 
anode,  and,  as  cathode,  a  thick  iron  wire.  With  this  com- 
paratively simple  outfit,  he  succeeded  in  obtaining  metallic 
calcium  in  large  well-fused  pieces,  capable  of  being  easily 
worked  with  a  file  or  hammer.  An  analysis  of  samples 
showed  99  per  cent,  calcium,  and  1  per  cent,  silicon,  but  no 
iron  or  aluminium. 

Arndt's  furnace  for  the  separation  of  metallic  calcium  by 
igneous  electrolysis,  consists  of  an  iron  crucible,  lined  in- 
teriorly with  a  paste  made  up  of  kaolin  and  water.  The 
base  is  additionally  protected  by  a  layer  of  calcium  fluoride, 
the  whole  being  dried  for  a  period  of  twenty-four  hours  in 
a  warm  place.  The  anode  is  a  carbon  rod,  and  the  cathode, 
an  iron  wire,  sheathed  to  within  4  c.m.  of  its  lower  extremity 
in  a  porcelain  tube. 

The  furnace  is  cooled  by  conduction  and  radiation,  being 
mounted,  for  that  purpose,  on  a  massive  cast-iron  base.  It 
is  filled  with  anhydrous  calcium  chloride,  and  the  action 
started  by  striking  an  arc  between  the  anode  and  an  inde- 
pendent carbon  rod  held  in  the  hand,  until  the  temperature 
has  risen  sufficiently  to  permit  the  current  to  flow  through 
the  alternative  path  provided  by  the  fused  electrolyte. 
The  current  is  then  maintained  constant  at  an  E.M.F.  of 
from  20  to  25  volts,  the  reaction  taking  place  quite  quietly. 
The  product  is  obtained  in  large  well  fused  masses,  a  fresh 
surface  of  which  is  nearly  white,  but  quickly  assumes  a 
yellowish  tinge.  The  metal  is  readily  workable,  and  is  of 
99  per  cent,  purity. 

Manganese,  and  its  alloy  with  iron,  commonly  known  as 
ferro-manganese,  has  lately  proved  a  subject  for  extensive 

209  p 


ELECTRIC   FURNACES   AND 


electric  furnace  operations,  both  experimental  and  industrial. 

The  Simon  electric  furnace  process  of  ferro-manganese 
manufacture,  which  has  been  successfully  applied  in  France, 
is  electrolytic.  It  consists  in  the  electrolysis  of  a  mass  of 
fused  calcium  fluoride,  in  which  oxide  of  manganese  has 
been  previously  dissolved.  In  this  respect  it  bears  a  re- 
semblance to  the  aluminium  extraction  processes  of  Heroult 
and  Hal). 

Careful  temperature  regulation  is  here,  as  in  many  other 
furnace  processes,  an  essential  feature  of  the  operation, 
metallic  manganese  being  volatile  at  a  temperature  but 
slightly  in  excess  of  its  melting  point. 

A  raw  charge  having  the  following  composition  is  fed 
into  the  furnace — 


Oxide  of  Manganese 
Silica     . 

Lime      .... 
Magnetic  oxide  of  Iron  . 


6  parts. 
6       „ 
3       ,. 

0-6  ,. 


Under  the  thermo-electrolytic  action  of  the  furnace,  the 
oxide  of  manganese  is  reduced  in  part  by  electrolysis,  and 
also  by  chemical  combination  of  its  oxygen  with  the  carbon 
of  the  electrodes.  The  results  are  found  to  be  most  favour- 
able when  carbon  is  mixed  with  the  oxide  before  its  intro- 
duction into  the  furnace.  The  product  has  the  following 
composition — 

Manganese  . 

Iron 

Silicon 

Carbon 

Phosphorus 

It  may  be  added  that,  should  silicon  and  phosphorus 
be  present  in  the  bath  as  impurities,  they  combine  with 
the  fluorine  as  the  result  of  secondary  reactions  and  pass 
off  as  volatile  by-products. 

The  above  process,  as  carried  out  in  practice,  involves  a 
power  expenditure  of  3,475  k.w.  hours  per  ton  of  ferro- 
manganese,  each  furnace  having  a  capacity  of  at  least 

210 


84-00  per  cent. 
8-30     „ 
0-20     „        „ 
7-10     ., 
0-10 


THEIR    INDUSTRIAL   APPLICATIONS 

150  k.w.,  and  a  terminal  E.M.F.  of  30  volts.  Of  this, 
only  7-5  volts  is  actually  required  to  effect  the  electrolysis, 
the  balance  being  neccessry  to  ensure  the  passage  of  the 
current  required  to  maintain  the  general  high  temperature 
of  the  mass. 

In  1902  it  was  decided  to  erect  a  plant  for  the  manu- 
facture of  ferro-manganese  by  this  method,  at  Orlu,  in  the 
Pyrenees.  The  cost  of  production,  with  cheap  water 
power  available,  was  estimated  at  £8  85.  Qd.  per  ton.  Further 
particulars  are  wanting. 

Metallic  Lead  has  been  prepared,  though  not  on  a  com- 
mercial scale,  by  electrolysis  of  its  fused  salts.  The  appa- 
ratus and  method  are  due  to  Borchers  ;  the  furnace  is  of 
cast  iron,  and  is  in  two  parts,  separated  from  one  another 
by  a  water-cooled  insulating  joint,  which,  by  virtue  of  its 
lower  general  temperature,  is  surrounded  and  protected 
from  the  action  of  the  fused  salt  and  metal  by  a  coating 
of  solidified  salt. 

One  side  of  the  furnace,  comprising  the  anode,  is  placed 
at  an  angle,  its  inner  surface  being  interrupted  by  a  series 
of  deep  horizontal  grooves  or  corrugations,  serving  to 
retain  a  portion  of  the  molten  lead,  which  is  constantly 
flowing  over  them  from  a  reservoir  above,  and  is  simul- 
taneously run  off  from  the  hearth  of  the  furnace  by  way 
of  a  siphon. 

The  furnace,  or  electrolytic  vat,  is  itself  placed  in  a  flue 
of  an  auxiliary  furnace,  which  maintains  its  contents  in  a 
state  of  fusion.  The  electrolyte  consists  of  a  mixture  of 
potassium  and  sodium  chlorides,  and  lead  oxy chloride  ; 
the  resultant  lead  collects  in  the  cathode  side  of  the  hearth, 
whence  it  is  continuously  removed  by  a  second  siphon. 

Borchers  employed  a  current  density  of  one  ampere  per 
square  centimetre,  at  a  pressure  of  0-5  volt,  the  yield  being 
5  kilogrammes  of  metallic  lead  her  1  e.h.p.  hour. 

Magnesium  is  produced  by  the  electrolysis  of  fused 
carnallite,  a  double  chloride  of  magnesium  and  potassium, 

211 


ELECTRIC   FURNACES   AND 

which  gives  up  its  water  of  crystallisation,  and  assumes  a 
clear  fluid  condition  at  a  temperature  below  700°C  = 
1,292°F.  The  electrolysis  is  carried  out  in  a  closed  cham- 
ber, an  inert  gas  being  passed  through  during  the  process. 
Chlorine  gas  is  evolved,  whilst  metallic  magnesium  is  set 
free,  and  floats  on  the  surface  of  the  electrolyte.  It  is 
essential  that  these  two  products  of  the  reaction  be  kept 
separate  from  one  another,  and  that  the  magnesium  be 
not  allowed  to  come  into  contact  with  oxygen,  hence  the 
necessity  for  passing  an  inert  gas  through  the  furnace 
chamber.  A  current  density  of  -15  ampere  per  square 
centimetre  of  cathode  cross-section  is  required  to  bring 
about  the  electrolysis. 

Zinc  — Borchers  has  experimented  on  the  extraction  of 
metallic  zinc  by  electrolysis  of  the  fused  chloride,  but  the 
process,  owing  to  certain  difficulties  in  the  way  of  its 
practical  application,  has  never  been  commercially  devel- 
oped. The  electrolytic  furnace  consisted  of  a  leaden  vessel, 
with  close-fitting  lid,  hermetically  sealed  in  position  by 
solidified  zinc  chloride.  A  zinc  lining,  bent  to  fit  the  interior 
of  the  crucible,  formed  the  cathode,  whilst  the  anode  con- 
sisted of  a  vertical  carbon  rod 

Means  were  provided  for  replenishing  the  charge  of  zinc 
chloride  and  conducting  away  the  chlorine  gas  evolved. 
Extraneous  heat  was  requisitioned  to  start  the  fusion, 
which  was  subsequently  maintained  by  the  passage  of  the 
current,  together  with  the  heat  of  the  reaction. 

M.  Gin  has  succeeded  in  preparing  Vanadium  and  its 
compounds  by  an  electrolytic  furnace  method  which  he 
described  in  a  paper  before  the  1903  International  Congress 
of  Chemistry  at  Berlin.  The  principle  of  the  process 
depends  upon  the  great  conductivity  of  vanadium  trioxide, 
and  on  the  facility  with  which  the  tri-fluoride  is  formed, 
when  the  trioxide  is  reacted  upon  by  fluorine  in  the  pre- 
sence of  carbon. 

The  most  important  preliminary  to  the  actual  process 

212 


THEIR    INDUSTRIAL    APPLICATIONS 

is  the  preparation  of  the  anodes.  Vanadium  trioxide, 
prepared  by  calcining  vanadic  acid  in  the  presence  of  carbon, 
is  mixed  with  a  suitable  proportion  of  retort  carbon  and 
powdered  resin,  and  the  mass  worked  up,  under  heat,  to 
a  plastic  paste.  The  latter  is  then  subjected  to  hydraulic 
pressure,  under  which  it  is  extruded  in  either  cylindrical 
or  prismatic  form,  through  dies. 

The  shaped  rods,  thus  formed,  are  then  subjected  to  a 
high  temperature  in  an  hermetically  sealed  oven.  The 
resultant  electrodes  are  said  to  be  capable  of  withstanding 
a  current  density  equal  to  0'7  of  that  of  carbon  electrodes 
of  the  same  section.  A  bundle  of  these  rods  constitutes 
the  anode,  whilst  the  cathode  is  a  block  of  iron. 

The  electrolyte  consists  of  fused  vanadium  fluoride, 
and,  under  the  action  of  the  furnace,  vanadium  is  set  free 
at  the  cathode  and  fluorine  at  the  anode.  The  latter  again 
enters  into  combination  to  form  a  fresh  quantity  of  vanadium 
fluoride,  and  the  electrolysis  is  repeated.  The  most  suitable 
current  density  is  said  to  be  2  amperes  per  square 
centimetre  of  anode  section,  and  6  amperes  per  square 
centimetre  of  cathode  section,  the  terminal  E.M.F.  being 
11  to  12  volts. 

For  alloys  containing  more  than  25  per  cent,  vanadium, 
the  cross  section  of  the  anode  should  be  appreciably  less 
than  the  total  active  surface  of  the  "anodes. 

Iron-vanadium  alloys,  and  an  increased  fluidity,  may  be 
obtained  by  adding  fluoride  of  iron  to  the  fused  mass,  but, 
if  no  iron  be  added,  almost  pure  vanadium  is  available, 
which,  however,  has  to  be  removed  from  the  furnace  in  a 
solid  state,  owing  to  the  difficulty  of  tapping  its  semi-liquid 
mass. 

The  equations  representing  the  two  stages  of  the  reaction 

are—  6F  +  V2O3  +  3C=2VF3  +  300 

and 


213 


ELECTRIC    FURNACES    AND 


SECTION  IX 

MISCELLANEOUS  ELECTRIC  FURNACE  PROCESSES 

"  Alundum"  as  distinguished  from  corundum  is  an 
electric  furnace  product,  the  process,  invented  by  Jacobs, 
being  exploited  by  the  Norton  Emery  Wheel  Company, 
of  Niagara  Falls,  who  utilize  some  500  H.P.  in  its  manu- 
facture, the  daily  yield  being  from  4  to  5  tons. 

The  process  consists  in  thoroughly  calcining  bauxite  in 
ordinary  furnaces,  after  which  it  is  fused  in  an  electric  furnace 
of  the  arc  type,  and  crystallizes,  on  cooling,  as  alundum. 

Baryta  is  another  electric  furnace  product.  It  is  manu- 
factured at  Niagara,  from  barytes,  by  the  United  Barium 
Company  ;  a  suitable  reducing  agent,  e.g.,  carbon,  is  added 
to  the  barytes,  and  the  mixture  subjected  to  electric  heat 
in  500  k.w.  furnaces,  from  which  the  product,  a  mixture  of 
oxide  and  sulphide  of  barium,  is  tapped  off. 

The  equations  representing  the  reactions  which  take 
place  are  as  follows — 

4BaSO4  +  4C=BaS  +  3BaSO4  +  4CO. 

The  barium  sulphide  then  reacts  with  the  sulphate, 
forming  anhydrous  baryta,  thus — 

BaS  +  3BaS04  =4BaO  +  4S02. 

The  mixed  product  is  separated  by  aqueous  solution,  the 
baryta  crystallizing  out  as  barium  hydrate  Ba(OH)2  +8  H20, 
whilst  the  sulphide  is  a  by-product. 

The  charge  consists  of  a  mixture  of  ground  barytes  and 
coke,  mixed  in  the  proportions  of  four  molecular  equiva- 
lents of  each.  When  heated  in  the  electric  furnace,  a 

214 


UNIVERSITY    I 


THEIR    INDUSTRIAL    APPLICATIONS 

reaction  occurs  between  the  carbon  and  barium  sulphate, 
according  to  the  above  equation,  25  per  cent,  of  the  latter 
being  reduced  to  barium  sulphide.  There  is  thus  created 
a  mixture  of  approximately  three  molecular  equivalents 
of  barium  sulphate  with  one  of  the  sulphide,  and  a  secondary 
reaction  occurs,  in  which  barium  hydrate  is  formed,  only 
2  to  3  per  cent,  of  unconverted  sulphate  remaining,  and 
a  small  quantity  of  the  sulphide. 

The  maximum  output  is  8  tons  of  product  per  24 
hours,  which  is  tapped  off  periodically,  and  dissolved 
in  hot  water.  The  insoluble  impurities  are  removed  by 
filtration,  and  the  barium  hydrate  crystallized  by  cooling, 
whilst  the  sulph-hydrate  remains  as  a  by-product. 

The  crystallized  barium  hydrate  is  washed  with  a  cold 
water  spray,  and  subsequently  dried  and  fused,  in  which 
latter  condition  it  is  poured  into  iron  drums,  and  solidifies, 
on  cooling,  into  masses  of  approximately  250  kgs.  apiece, 
containing  less  than  1  per  cent,  of  impurities. 

The  principal  applications  of  barium  hydrate  are  in  the 
sugar  industry,  water  purification,  tanning,  and  the  manu- 
facture of  pigments. 

The  plant  of  the  United  Barium  Company  at  Niagara 
has  a  capacity  of  60  tons  of  the  hydrate. 

Barium  Cyanide  is  another  commercial  electric  furnace 
product.  It  is  manufactured  by  the  Cyanide  Company  at 
Niagara  Falls.  As  a  raw  material,  barium  carbide,  mixed 
with  coke,  is  used,  and  subjected  to  heat  in  the  electric 
furnace,  whilst,  at  the  same  time,  a  current  of  producer 
gas  is  passed  through  the  mixture,  with  the  result  that 
the  necessary  combination  with  nitrogen  is  secured. 

Calcium  Cyanide. — A  patent  has  been  taken  out  by  a 
German  Company,  on  an  electric  furnace  process  for  the 
production  of  *  calcium  cyanide.  A  mixture  of  lime  and 
coke  is  raised  to  a  temperature  of  2,000°C.=  3,632°F., 
whilst  nitrogen  gas,  or  air,  is  passed  over  the  mixture.  The 
necessary  proportion  of  nitrogen  enters  into  chemical  com- 

215 


ELECTRIC   FURNACES   AND 

bination  with  these  ingredients  to  form  the  cyanide,  which 
is  stated  to  be  of  value  as  a  fertiliser. 

An  electric  furnace  process,  for  the  casting  of  articles  from 
refractory  materials,  e.g.,  fire-bricks,  tiling,  conduits,  etc., 
has  been  devised  by  Mr.  Chas.  B.  Jacobs.  It  consists  in 
subjecting  acid  silicates,  such,  for  example,  as  the  compound 
represented  by  the  formula  A1203.  2Si02,  to  continued  fusion 
in  any  ordinary  electric  furnace.  As  a  result,  a  certain  pro- 
portion of  the  silica  is  volatilized,  and  the  residue,  a  tough 
mass,  of  waxy  appearance,  having  distinct  physical  properties, 
may  be  run  into  moulds  of  any  desired  form. 

As  an  example  of  the  energy  necessary  to  effect  the  fusion, 
it  is  stated  that  a  current  of  1,500  amperes  at  100  volts 
will  suffice  to  melt  90  kgs.  of  the  charge  in  20  minutes,  the 
continuation  of  the  fusion  for  another  40  minutes  being 
sufficient  to  volatilise  50  per  cent,  of  the  silica. 

Silicides. — The  silicides  of  the  alkaline  earth  metals, 
calcium  silicide  (CaSi2),  barium  silicide  (BaSi2),  and 
strontium  silicide  (SrSi2),  were  discovered  by  the  Ampere 
Electro-Chemical  Company,  in  July  1899.  They  are  the 
silicon  analogues  of  the  alkaline  earth  carbides,  and  are 
manufactured  in  the  electric  furnace  under  similar  conditions, 
though  at  a  rather  higher  temperature  than  is  called  for  hi 
the  formation  of  the  carbides. 

The  raw  materials  consist  of  carbonates,  oxides,  sul- 
phates, or  phosphates  of  the  alkaline  earth  metals,  mixed 
with  silica  and  carbon,  in  the  requisite  proportions  to  bring 
about  the  reduction  ;  or,  as  an  alternative  mixture,  silicates 
of  calcium,  barium,  and  strontium,  mixed  with  sufficient 
carbon  to  combine  with  the  oxygen  present  in  the  compounds. 

The  resultant  silicides,  according  to  Jacobs,  are  white, 
or  bluish  white,  of  metallic  appearance,  and  with  a  distinct 
crystalline  structure.  They  oxidise  slowly  in  air,  at  normal 
temperatures,  and  more  rapidly  when  heated,  yielding  silicon 
dioxide,  and  the  oxide  of  the  particular  alkaline  earth  metal 
content. 

216 


THEIR    INDUSTRIAL    APPLICATIONS 

Like  the  carbides,  they  decompose  when  brought  into 
contact  with  water,  evolving  hydrogen  gas,  according  to  the 
equation — 

BaSi2  +  6H20=Ba(OH)2-2Si02  +10H. 

The  following  are  the  quantities  of  hydrogen  gas,  which 
are  obtainable  from  one  pound  of  chemically  pure  silicides, 
on  treatment  with  water — 

One  pound  calcium  silicide    .          .  .  18-73  cubic  feet 

,,         ,,         strontium  silicide  .  .  12-36     ,,         ,, 

,,         ,,  •      barium  silicide     .          .  .        9-15     ,,         ,, 
at  0°C.  =  32°F.,   and    760mm.  pressure. 

As  a  hydrogen  producer,  barium  silicide  is  stated  to  be 
the  cheapest  and  most  convenient  source,  it  being  only 
necessary  to  introduce  the  material  into  an  ordinary  acety- 
lene gas  generator,  and  decompose  with  water  in  the  usual 
way. 

All  the  silicides  are  strong  reducing  agents,  and  that  of 
barium  has  been  largely  used  for  the  reduction  of  indigo  by 
making  the  indigo  blue  into  a  thin  paste  with  water,  and 
introducing  the  barium  silicide,  which  has  been  previously 
ground  fine ;  the  solution  of  indigo  white,  thus  produced, 
may  be  applied  directly  to  the  fibre  of  the  substance  to  be 
dyed. 

If  kaolin,  or  china  clay,  be  subjected  to  heat  in  the  electric 
furnace,  and,  simultaneously,  to  the  action  of  a  current  of 
hydrogen  gas,  silicon  hydride  is  formed,  according  to  the 
equation — 

Al2Si2O7  +  8H  =  SiH4  +  2H20  +  Al2Si06. 

If  continued  still  further,  the  reaction  results  in  the  re- 
duction of  the  aluminium  silicate  to  aluminium  oxide,  either 
of  which  are  of  value  as  abrasives.  The  silicon  hydride 
ignites  spontaneously  on  coming  into  contact  with  air, 
forming  silicon  dioxide  and  water  vapour.  The  former, 
being  in  a  state  of  extreme  comminution,  is  valuable  as  a 
polishing  powder  for  fine  metal  work. 

Combination  Processes. — Several  inventors  in  the  electric 

217 


ELECTRIC    FURNACES    AND 

furnace  field  have  essayed  to  combine,  efficiently  and  practi- 
cally, two  processes  in  one  and  the  same  operation,  using 
the  same  furnace  structure,  and  collecting  the  products 
independently.  Such  combination  methods  can  hardly  be 
regarded  as  successful  in  a  commercial  sense,  in  that  the 
conditions  essential  to  one  process  are  seldom,  if  at  all, 
allied,  or  in  any  way  similar  to  those  governing  the  successful 
conduct  of  another. 

The  natural  consequences  of  an  attempt  to  combine  two 
such  processes  in  one  and  the  same  operation  are  therefore 
impracticable  complication  of  the  furnace,  and  commercial 
inefficiency  of  one  or  both  processes. 

An  instance  of  such  combination  methods  is  that  suggested 
by  Mr.  A.  Dorsemagen,  of  Wesel,  Germany,  for  combining 
carborundum  manufacture  and  the  reduction  of  zinc  ores. 
In  order  to  effect  this,  silicate  of  zinc  is  substituted  for  the 
sand  of  the  usual  carborundum  furnace  charge,  with  the 
result  that  carborundum  is  formed  in  the  usual  way,  or  said 
to  be  formed,  whilst  the  metallic  zinc,  liberated  from  com- 
bination with  the  silica,  distils  over  into  a  suitable  receiver. 

In  order  to  bring  about  this  double  reaction,  a  special 
form  of  furnace  construction,  differing  materially  from  the 
ordinary  open  carborundum  furnace,  is  an  obvious  necessity  ; 
such  a  furnace  must  be  closed  in  on  all  sides,  and  the 
material  of  its  walls  must  be  impervious  to  zinc  vapours. 
It  seems  hardly  likely  that  the  manufacture  of  carborundum, 
comparatively  inefficient  as  is  the  simple  procedure  at 
present  adopted,  would  prove  commercially  feasible 
if  worked  in  conjunction  with  the  electrical  reduction  of 
zinc  ore,  which  latter  is,  to  electro-metallurgists,  still  in 
the  nature  of  a  partially  solved  problem. 

Other  combined  electric  furnace  processes  worthy  of 
mention,  are  that  of  Rathenau,  for  the  manufacture  of  iron 
silicides  by  the  addition  of  iron  to  the  charge  of  a  calcium 
carbide  furnace  ;  this  method,  which  has  for  its  object, 
the  purification  of  the  resultant  carbide,  has  already  been 

218 


THEIR    INDUSTRIAL    APPLICATIONS 

described,  and  cannot  be  regarded  in  the  light  of  a  commercial 
failure,  in  that  it  effects  the  desired  object,  whilst  the  by- 
product is  useful,  and  does  not  involve  unnecessary  com- 
plication of  the  furnaces. 

The  same  applies  to  Heibling's  simultaneous  manufacture 
of  chrome-iron  and  calcium  carbide,  which  is  also  a  purifi- 
cation method  pure  and  simple  ;  the  latter,  which  forms  as 
a  slag,  depriving  the  chrome-iron  of  carbon  as  an  undesirable 
impurity. 

Desjardins  has  also  proposed  the  joint  production  of  water 
glass  and  phosphorus  by  treating,  in  the  electric  furnace, 
a  mixed  charge  of  sodium  phosphate,  silica,  and  carbon. 

Joudrain,  Billaudot,  Jacobsen,  Hilbert,  Bradley,  Read, 
and  Jacobs,  have  patented  joint  processes  for  the  simul- 
taneous manufacture  of  calcium  carbide  and  phosphorus. 
The  process,  in  general,  consists  in  treating  calcium  phos- 
phate in  the  furnace  with  excess  of  carbon,  the  latter  reacting 
with  the  calcium  to  form  carbide,  and  the  liberated  phos- 
phorus distilling  over. 

The  disadvantages  incidental  to  such  a  combination  are, 
that  in  addition  to  complicating  the  carbide  furnace  construc- 
tion, calcium  phosphide  is  formed  conjointly  with  the  carbide, 
and  any  acetylene  gas  subsequently  generated  from  the 
latter  is  contaminated  with  phosphoretted  hydrogen. 

The  last  three  inventors  enumerated  above  recognize 
this  fact,  and  claim,  in  their  patent  specification,  the  manu- 
facture of  calcium  "  carbophosphide,"  a  mixture  of  carbide 
and  phosphide  of  calcium  in  such  proportions  that,  when 
reacted  upon  by  water,  a  spontaneously  inflammable  mix- 
ture of  gases  is  produced.  This  compound  is  especially 
suitable  for  the  "  marine  light,"  a  modern  auxiliary  in 
naval  and  military  operations,  and  is  therefore  in  demand. 

M.  Gustav  Gin,  whose  name  is  associated  with  modern 
research  into  the  possibilities  of  electric  smelting,  has  de- 
vised a  joint  process  for  the  simultaneous  production  of  iron 
alloys,  and  alkaline  oxides  ;  e.g.,  ferro-silicon  and  baryta. 

219 


ELECTRIC    FURNACES    AND 

The  process  is  carried  out  in  two  stages,  the  first  of  which 
does  not  necessarily  entail  the  use  of  an  electric  furnace 
in  that  a  very  high  temperature  is  not  required.  A  mixture 
of  broken  quartz,  barium  sulphate,  and  charcoal,  is  sub- 
jected to  moderate  heat,  with  the  resultant  formation  of 
barium  silicate.  The  latter  is  then  mixed  with  metallic 
iron  or  its  oxide,  and  carbon,  and  again  subjected,  this 
time  to  a  high  temperature,  in  the  electric  furnace.  Ferro- 
silicon  and  barium  oxide  are  formed,  the  latter  being  col- 
lected as  a  sublimate. 

An  English  patent,  dated  May  9,  1901,  was  granted  to 
A.  H.  Cowles  and  the  British  Aluminium  Company  on  a 
double  electric  furnace  process,  in  which  an  alloy,  or  carbide 
of  aluminium,  and  metallic  sodium,  are  produced  simul- 
taneously in  one  operation  of  the  furnace. 

The  latter  has  one  wall  which  is  pervious  to  gases,  and 
forms  a  partition  between  the  furnace  proper  and  a  con- 
densing chamber,  where  the  metallic  sodium  is  collected. 
In  the  furnace  is  placed  a  mixture  of  sodium  aluminate 
and  carbon ;  under  the  influence  of  electrical  heat  the 
sodium  is  set  free,  and  passes,  as  a  vapour,  through  the 
porous  wall  into  the  condensing  chamber,  where  it  is  duly 
condensed  and  collected  as  metallic  sodium  The  aluminium 
combines  with  the  carbon  to  form  aluminium  carbide,  or, 
if  a  non- volatile  metal  be  present,  unites  with  it  to  form 
an  alloy.  An  alloy  of  sodium  may  be  similarly  produced 
by  including  a  volatile  metal  among  the  constituents  of 
the  furnace  charge. 


220 


THEIR    INDUSTRIAL   APPLICATIONS 


SECTION  X 

LABORATORY  FURNACES  AND  EXPERIMENTAL  RESEARCH 

Some  interesting  and  instructive  laboratory  furnaces  for 
experimental  use  have  been  designed  for,  and  are  in  use 
at,  Owens  College,  Manchester. 

They  were  aptly  described  and  illustrated  in  a  paper 
read  by  Prof.  R.  S.  Hutton  before  a  meeting  of  the  Institu- 
tion of  Electrical  Engineers,  November  25,  1902. 

A  40-kilowatt  Moissan  arc 
furnace,  which  is  typical  of  arc 
furnaces  with  indirect  or  re- 
flected heat,  is  shown  in  sec- 
tion in  Pig.  48.  It  consists  of 
two  blocks,  A  and  B,  of  Monk's 
Park  bath  stone,  one,  A,  form- 
ing the  cover,  or  domed  lid, 
and  the  other,  B,  the  body  of 
the  furnace. 

These  two  blocks  are  grooved 
semi-circularly  where  they  fit 
together,  in  order  to  form  a 
circular  channel  for  the  recep- 
tion of  the  carbon  electrodes  E  E,  which  pass  hori- 
zontally through  the  walls,  and  meet  at  the  centre,  with  the 
exception  of  an  arcing  space,  which  is  situated  just  above 
the  centre  of  the  recess  or  hearth  in  the  lower  block  B. 
This  latter  is  from  2J  to  4  in.  in  diameter,  and  in  it  is 
placed  a  carbon  crucible  C,  resting  on  a  layer  of  powdered 
magnesia,  which  isolates  it  from  contact  with  block  B. 
A  clearance  space  is  also  left  around  the  crucible  as  shown  ; 

221 


FIG.  48. 


ELECTRIC    FURNACES    AND 

this  facilitates  the  heating,  and  also  prevents  combination 
between  the  carbon  of  the  crucible  and  the  limestone, 
which  might  otherwise  take  place  under  the  influence  of 
the  intense  heat  generated.  F  F  are  iron  bands,  which 
serve  to  hold  the  blocks  together,  and  prevent  them  from 
splitting,  whilst,  at  the  same  time,  they  afford  a  ready 

means  of  lifting  either  the 
entire  furnace,  or  its  cover, 
by  means  of  attached  eye- 
bolts.  The  remaining  di- 
mensions of  the  furnace  are 
indicated  in  the  sketch. 

Another  form  of  experi- 
mental arc  furnace  in  use 
at  Owens  College  comprises 
a  vertical  construction, 
which,  with  some  slight 
and  easily  effected  modifi- 
cations, can  be  adapted  to 
a  variety  of  purposes.  It 
is  represented  in  Fig.  49, 
and  consists  of  a  rect- 
angular cast-iron  base,  B, 
some  19  in.  long,  by  14  in. 
wide,  strengthened  by  cross 
ribs  cast  on  to  it  belqw, 
FIG.  49.  and  provided  at  one  corner 

with  a  levelling  screw,  and 

at  the  other  with  a  |-in.  clamping  bolt,  to  serve  as  a  ter- 
minal connexion. 

Rising  vertically  from  the  centre  of  one  of  the  lesser  sides 
of  this  base,  is  a  hollow  cast-iron  standard,  S,  2J  in.  in 
diameter,  flanged  at  its  lower  extremity,  and  bolted  to  the 
base  B,  a  sheet  of  vulcanized  fibre  F  being  interposed  for 
the  purpose  of  insulation.  A  steel  plunger  P,  IJin.  in 
diameter,  fits  inside  this  standard,  and  is  capable  of  vertical 

222 


THEIR    INDUSTRIAL    APPLICATIONS 

adjustment  therein,  being  firmly  secured  in  any  desired 
position  by  the  hand  wheels  and  set  screws  W  W  Clamped 
at  right  angles  to  the  upper  extremity  of  this  plunger  is  a 
cross  bar  or  bracket  A,  which  carries,  at  its  outer  end,  the 
screw  feed  adjustment  H,  and  clamp  K,  of  the  upper 
carbon  D.  Means  for  two  terminal  connexions  to  the 
pillar  and  carbon  holder  are  provided,  that  shown  at  a 
being  employed  in  cases  where  the  current  exceeds  600 
amperes. 

The  carbon  holder  K  is  fitted  with  a  set  of  clamping 
collars  of  varying  diameter,  which  will  accommodate  car- 
bons up  to  3  in.  ;  it  is  carried  by  a  phosphor  bronze  stem 
T,  1 J  in.  in  diameter,  and  square  threaded  (four  to  the  inch) 
for  feed  adjustment.  About  12  in.  vertical  adjustment 
is  obtainable  through  this  construction,  and  is  effected 
by  means  of  the  hand  wheel  J.  The  electric  circuit  to  the 
upper  carbon  is  not  completed  through  the  screw  threads 
and  bushing,  but  is  provided  by  four  \  in.  flexible  cables 
c  c  clamped  to  a  lug  L  cast  on  the  bracket,  and  to  the 
upper  extremity  of  the  phosphor-bronze  stem. 

The  hearth  or  crucible  may  be  varied  to  suit  the  opera- 
tion it  is  required  to  perform,  and  is  supported  on,  or  clamped 
to  the  cast-iron  base  B,  with  its  centre  immediately  in  line 
with  the  axis  of  the  upper  carbon  electrode. 

A  40-kilowatt  experimental  carbide  furnace,  with 
parallel  electrodes  is  also  described  by  Prof.  Hutton.  It 
is  a  very  simple  affair,  as  the  diagram,  Fig.  50,  will  indi- 
cate. E  E  are  the  two  parallel  electrodes  clamped 
side  by  side,  but  insulated  from  one  another  in  a  cross-bar 
or  yoke  B.  Electrical  connexion  with  the  carbons  is 
secured  by  flat  copper  straps  c  c,  which  also  serve  as 
supports  for  the  carbons  and  yoke  piece,  and  are  slung,  by 
a  second  upper  yoke,  to  a  crane  C.  They  slide  in  recesses 
provided  for  them  in  the  bracket  D,  and  are  thus  pre- 
vented from  swaying.  The  furnace  hearth  is  either  built 
up  of  fire-brick,  or  takes  the  form  of  a  cast-iron  pot,  the 

223 


ELECTRIC   FURNACES    AND 


FIG.  50. 


material  under  treatment 
providing  a  sufficiently  re- 
fractory lining. 

A  novel  feature  of  the 
laboratory  equipment  at 
Owens  College,  consists  in  a 
high  pressure  electric  furnace, 
which  can  be  adapted  to 
any  of  the  many  and  varied 
electric  furnace  processes, and 
is  designed  to  operate  under 
a  pressure  of  200  atmospheres. 
It  consists  of  a  massive  steel 
cylinder  which  can  be  used 
either  in  a  horizontal  or  vertical  position. 

Screw  gearing,  actuated  through  high  pressure  glands, 
serves  to  feed  the  electrodes  together  inside,  whilst  two 
small  windows  at  opposite  ends  of  a  diameter  are  constructed 
to  withstand  the  maximum  pressure,  and  permit  inspection 
of  the  interior  during  the  progress  of  an  experiment,  or 
may  be  replaced,  if  so  desired,  by  gas  inlet  and  outlet  pipes, 
where  it  is  desired  to  conduct  an  operation  in  an  atmosphere 
of  any  given  gas.  The  whole  cylinder  is  water- jacketed, 
the  actual  hearth  of  the  furnace  consisting  of  a  refrac- 
tory lining  contained  within,  and  supported  by  a  cast- 
iron  enclosure,  between  which  and  the  outer  steel 
cylinder  the  water  circulation  takes  place. 

Suitable  valves  and  pressure  gauge  connexions  are  also 
provided. 

The  furnace  was  constructed  by  Messrs.  Lennox,  Reynolds, 
and  Fyfe,  to  designs  provided  by  the  College  authorities. 

The  Physical  Chemistry  department  of  the  McGill 
University,  Montreal,  is  equipped  with  two  electric 
furnaces.  They  have  a  current  capacity  of  100  amperes 
at  110  volts,  and  are  principally  employed  in  the  analysis 
of  refractory  compounds. 

224 


THEIR    INDUSTRIAL    APPLICATIONS 


A  convenient  resistance,  crucible  furnace,  for  the  deter- 
mination of  the  cooling  curves  of  steel,  and  of  melting  points, 
has  been  devised  by  H.  M.  Howe,  Ph.D.,  for  the  School 
of  Mines,  Columbia  University. 

It  is  represented  in  sectional  elevation  by  Fig.  51,  and 
consists  of  a  cylindrical  structure  M  of  magnesia,  made 
in  two  semi-cylindric  halves  in  order  to  permit  ready  access 
to  the  interior,  in  which  is  placed  the  magnesia  crucible  C. 
Surrounding  this  crucible,  and  embedded  in  a  groove  in  the 
magnesia  blocks  M,  specially  prepared  for  its  reception, 
is  a  spiral  platinum  coil  P,  of 
U-shaped  section,  the  edges  of 
the  U  fitting  closely  against  the 
outer  wall  of  the  crucible.  The 
extremities  of  this  heating  spiral 
are  led  out  of  the  furnace  at 
a  and  b  for  connexion  to 
suitable  terminals,  whilst  an 
inlet  pipe  p  provides  for  the 
introduction  of  any  desired  gas 
into  the  interior  of  C.  A 
magnesia  lid  L  is  fitted  over 
the  top,  and  luted  on  with  fire- 
clay. S  is  a  removable  stop- 
per, making  a  fairly  close  joint 

with  the  lid,  and  serving  for  the  introduction,  through  a 
central  vertical  bore,  of  the  insulated  and  protected  twin 
leads  I  of  the  thermo-couple  T,  which,  situated  in  the 
centre  of  the  crucible,  and,  consequently,  of  the  heat  zone, 
serves  to  indicate  the  temperature. 

Small  leakages  through  the  various  points  of  entry  of 
the  platinum  wires  and  thermo-couple  connexions  are 
counterbalanced,  in  the  main,  by  packing,  and  also  by 
maintaining  a  suitable  pressure  of  gas  at  the  inlet  pipe  p. 

A  special  taper  mandrel,  grooved  to  correspond  with  the 
interior  groove  in  the  magnesia  blocks  M,  is  utilized  for 

225  Q 


ELECTRIC    FURNACES    AND 

the  introduction  of  the  spiral,  the  two  halves  of  M  being 
brought  together  so  as  to  encircle  it,  and  the  mandrel  itself 
subsequently  withdrawn  by  a  left-hand  screw  motion, 
leaving  the  wire  in  its  place  in  the  groove. 

A  simple  and  convenient  form  of  electric  oven,  or  furnace 
for  dentists  and  laboratory  use,  is  the  invention  of  Mr. 
August  Eimer.  It  takes  the  form  of  a  rectangular  base 
plate  and  semi-cylindrically  domed  cover,  both  of  re- 
fractory material.  One  end  is  permanently  closed  by  a 
semi-circular  plate,  which  forms  the  back  of  the  furnace, 
whilst  the  front,  which  is  removable,  is  vertically  mounted 
at  the  end  of  a  sliding  plate,  which  covers  the  furnace  hearth, 
and  serves  as  a  container  or  tray,  for  the  reception  of  the 
articles  to  be  heated  ;  it  is  removed,  bodily,  with  the  front 
door  of  the  furnace,  in  the  centre  of  which  is  an  inspection 
aperture. 

The  heating  elements  consist  of  wires  threaded  back- 
wards and  forwards,  at  regular  intervals,  through  longitu- 
dinal holes  in  the  thickness  of  the  domed  cover.  A  sliding 
base  plate,  fitting  inside,  and  constituting  the  hearth  of  the 
oven,  also  carries  similar  wires  embedded  in  it. 

The  Hammond  dental  muffle,  invented  by  Dr.  J.  F. 
Hammond,  is  not  based  on  any  new  fundamental  principle, 
its  novelty  lying  more  in  the  elaboration  of  detail,  and  pro- 
vision for  interchangeability  of  parts,  and  consequent  free- 
dom from  serious  breakdown. 

It  is  heated  on  the  resistance  principle,  the  heater  being 
a  platinum  wire  coil,  embedded  in,  and  protected  by,  a  fire- 
clay foundation.  The  heat  developed  is  retained  by  a 
heat-conserving  jacket,  consisting  of  alternate  layers  of 
sand,  fire-clay,  and  metal,  arranged  concentrically  round 
the  central  hearth.  A  mica  door  is  provided  for  convenience 
in  the  introduction  of  the  objects  to  be  heated,  and  also 
provides  a  ready  means  of  watching  the  process,  whilst  the 
whole  is  mounted  on  a  convenient  base  with  the  necessary 
controlling  resistance  and  switch. 

226 


THEIR    INDUSTRIAL    APPLICATIONS 

The  principle  novelty  consists  in  the  arrangement  of  the 
resistance  coil  itself,  which  is  provided,  at  regular  and  fre- 
quent intervals  with  loops,  projecting  outwards  through 
the  walls  of  the  furnace. 

These  loops  permit  the  necessary  expansion  and  contraction 
of  the  wire,  due  to  heating  and  cooling,  whilst  any  incidental 
interruption  in  the  circuit  is  readily  located  and  repaired. 

A  resistance  muffle,  invented  by  J.  Weiss,  presents  some 
points  of  similarity  to  the  laboratory  crucible  of  H.  M.  Howe, 
described  in  another  paragraph.  It  has,  for  its  object, 
the  rendering  of  all  parts,  such  as  are  subject  to  wear  and 
tear,  readily  accessible  for  repair  and  replacement.  To  this 
end,  the  muffle  itself,  which  is  tubular  in  form,  with  the 
platinum  resistance  wire  wound  in  a  groove  around  its 
outer  periphery,  is  encased,  bodily,  in  a  foundation  block, 
which  is  divided,  vertically,  into  two  halves,  along  a  plane 
corresponding  with  the  axis  of  the  muffle.  The  latter  is 
flanged  at  its  two  extremities,  the  flanges  fitting  into  cor- 
responding recesses  in  the  supporting  block,  whilst  a  recess 
in  each  block,  somewhat  larger  than  the  outer  diameter 
of  the  muffle,  provides  an  air-space,  and  prevents  undue 
heating  of  the  casing,  such  as  would  otherwise  result  from 
direct  contact  with  the  platinum  resistance. 

The  extremities  of  the  latter  are  led  out  to  terminals 
on  the  upper  surface  of  one  of  the  two  casing  blocks,  and 
the  whole,  when  mounted  up  and  ready  for  operation,  is 
held  together  by  a  suitable  frame  or  strap,  furnished  with  a 
set  screw. 

In  the  form  of  dental  muffle,  or  laboratory  resistance 
furnace,  devised  by  R.  Winter,  a  considerable  reduction 
in  the  size  of  the  heating  units,  and  correspondingly  lessened 
liability  to  fracture  under  extreme  variation  of  tempera- 
ture, are  secured  by  embedding  the  resistance  wires  in 
porcelain  tubes,  and  supporting  the  latter  in  horizontal 
grooves  in  opposite  interior  walls  of  the  furnace,  even 
spacing  being  secured  by  lateral  projections. 

227 


ELECTRIC    FURNACES    AND 

The  electric  furnace  in  miniature  has  been  adapted  to 
the  requirements  of  microscopical  research.  The  apparatus 
was  described  by  Prof.  C.  Doelter  to  the  Vienna  Academy 
of  Sciences.  An  electric  oven,  2  in.  high,  is  mounted 
on  the  object  stand  of  the  microscope,  and  yields  tempera- 
tures up  to  1,200°C.=2,192°F.  In  use,  the  lens  is  separated 
from  the  heated  object  by  about  1  in.  Even  at  the 
highest  temperature  of  the  subject  under  examination, 
however,  both  microscope  and  objective  are  kept  quite 
cool  by  a  special  arrangement  of  asbestos  plates,  and  a 
spiral  tube  carrying  ice-cold  water. 

A.  Kalahne  has  experimented  with  various  stoves  of 
the  embedded  resistance  type,  with  a  view  to  determining 
their  limitations,  and  energy  consumption.  The  results 
of  his  researches  were  published  in  Ann.  der  Physik,  No.  6, 
1903,  in  the  form  of  graphic  curves,  of  which  the  verti- 
cal ordinates  represented  watts  consumed,  and  the  hori- 
zontal ordinates,  temperatures  attained,  in  degrees  Centi- 
grade. 

Six  different  furnaces  were  tested,  of  which  two  were 
provided  with  double  coils,  whilst  the  remaining  four  had 
only  one  coil  apiece.  As  regards  the  foundations,  or  bodies 
of  the  furnaces,  which  were  in  tube  form,  five  were  of  porce- 
lain, 40  to  70  c.m.  long,  three  being  glazed  interiorly,  but 
not  exteriorly.  A  sixth  tube,  20*2  c.m.  in  length,  was  of 
Marquardt  composition. 

Kalahne  found  asbestos  a  preferable  material  to  fire- 
clay for  covering  in  the  resistance  wires,  which  were  of 
nickel.  If  fire-clay  be  employed,  its  different  coefficient 
of  expansion  leads  to  cutting  or  tearing  of  the  resistance 
wire  at  high  temperatures.  Asbestos  possesses  the  ad- 
ditional recommendation  that  it  can  be  easily  renewed. 

Application  of  the  Electric  Furnace  to  Scientific  Research. — 
By  no  means  the  least  important  of  the  many  uses  to  which 
the  electric  furnace  has  been  applied  is  that  of  an  auxiliary 
to  scientific  research,  especially  among  such  refractory 

228 


THEIR    INDUSTRIAL    APPLICATIONS 

substances  as  the  diamond,  and  metals  with  exceedingly 
high  melting  points. 

As  an  example  of  what  can  be  done  with  the  aid  of  electric 
heat,  tantalum,  which  has  hitherto  been  known  only  as 
a  somewhat  impure  powder,  having  a  density  of  10' 50, 
has  now  been  produced  from  tantalic  acid  in  the  electric 
furnace  by  Henri  Moissan.  The  acid  was  reduced  to  metallic 
tantalum  by  heating  electrically  in  the  presence  of  sugar 
carbon  as  a  reducing  agent,  and  the  product,  which  shows 
a  density  of  12' 7 9,  has  a  brilliant  metallic  lustre.  It 
scratches  quartz,  is  infusible  in  the  oxy-hydrogen  blow- 
pipe flame,  has  a  crystalline  fracture,  and  is  classed  with 
the  metalloids. 

At  the  Fifth  International  Congress  of  Applied  Chemistry, 
held  in  Berlin,  W.  Hempel  described  some  experiments 
on  melting-point  determinations  at  high  temperatures, 
which  had  been  carried  out  with  the  aid  of  an  electric 
furnace  built  up  of  carbon  rods  surrounded  by  Kieselguhr. 
With  this  apparatus  the  melting-point  of  magnesia  was 
found  to  be  in  the  neighbourhood  of  2,250°C.=  4,082°F., 
and  of  lime,  1,900°C.—  3,452°F. 

With  the  Heraeus  platinum-foil  tube  furnace  the  melting- 
point  of  99  per  cent,  manganese  was  investigated  and 
found  to  be  1,245°C.=  2,273°F. 

The  Heraeus  platinum-foil  tube  furnace,  and  the  new 
quartz  tubes,  supplied  by  Heraeus,  of  Hanau,  and  by  Siebert 
and  Kuhn,  of  Cassel,  have  provided  means  for  the  conduct 
of  numerous  experiments  on  the  volatilization  of  metals, 
hitherto  impossible  with  glass  tubes. 

The  advantages  of  quartz  for  this  purpose  are — 

1.  That  it  will  stand  a  very  high  temperature  without 
softening,    and   vessels   made   of   it   can   consequently   be 
exhausted   of   air,    even   when   simultaneously   subject   to 
extremely  high  temperatures. 

2.  One  portion  of  a  quartz  vessel  may  be  cooled  whilst  the 
other  is  glowing,  thus  rendering  it  possible  to  evaporate 

229 


ELECTRIC    FURNACES    AND 

metals  in  the  hotter  region  of  the  tube,  and  condense  them 
in  the  cooler  portion,  without  risk  of  fracture,  whilst  gas- 
tight  connexions  with  the  cooler  portions  can  be  made 
with  the  aid  of  a  mixture  of  two  parts  wax  and  one  part 
wool  grease. 

Metals,  per  se,  do  not  attack  quartz,  but  their  oxides 
do,  so  that  a  certain  amount  of  care  is  essential,  especially 
in  dealing  with  lead. 

The  quartz  vessels  are  L-shaped,  and  the  metal  is,  as 
a  rule,  placed  in  a  bulb,  blown  to  the  top  of  the  L,  and 
bent  back. 

With  this  apparatus  Drs.  F.  Krafft,  Kuch,  and  Haa-gn, 
of  Hanau,  have  conducted  a  series  of  experiments  to  deter- 
mine the  boiling,  volatilization,  and  distillation  tempera- 
tures of  various  metals.  The  full  text  of  their  researches 
is  published  in  the  Berichte  der  Deutschen  Chemischen  Gesell- 
schaft,  vol.  XXXVI.  The  vacuum  employed  is  described 
as  one  suitable  for  cathode  glows,  whilst  the  temperatures 
were  determined  by  the  aid  of  platinum — platinum-rhodium 
thermo-couples. 

The  following  are  a  few  of  the  more  interesting  results 
obtained  by  these  investigators  :  Zinc  began  to  distil  dis- 
tinctly at  430°C.=  806°F.  without  melting,  and  distillation 
afterwards  continued  at  a  temperature  of  300°C.  =  572°F. 
The  boiling  zinc  displayed  the  Leiden-frost  phenomenon, 
which  was  also  observed  in  the  case  of  cadmium.  The 
latter  began  to  evaporate  at  320°C.=  608°F.,  and  dis- 
tilled visibly  at  448°C.  =  838°F.  Selenium  was  easily 
volatilized  at  380°C.=  716°F.  TeUurium  distilled  and 
boiled  briskly  at  540°C.  =  1,004°F.  ;  lead  volatilized 
sufficiently  at  801°C.=:  1,472°F.,  to  form  a  mirror  which 
could  be  melted,  and  at  1,160°C.=  2,120°F.  it  boiled 
regularly  and  distilled.  Antimony  was  volatilized  at 
670°C.=  1,238°F.,  and  distilled  at  780°C.=  1,436°F.  ; 
bismuth  volatilized  at  540°C.=:  1,004°F.,  and  distilled 
at  1,140°C.=  2,084°F.  ;  tin  could  not  be  volatilized  at 

230 


THEIR    INDUSTRIAL    APPLICATIONS 

1,100°  C.=  2,012°F.,  however.  Silver  began  to  volatilize 
at  1,200°C.:=2,1920F.  ;  at  1,340°C.=  2,444°F.  it  distilled 
at  the  rate  of  0'09  grammes  in  12  minutes.  Copper  began 
to  distil  at  1,315°C.=  2,399°F.  Gold  was  the  most  refrac- 
tory metal  experimented  with  ;  it  formed  a  mobile  liquid 
at  1,180°C.=  2,156°F. ;  at  1,300°C.=  2,372°F.  some  silver 
distilled  over  from  the  impure  gold,  whilst  at  1,375°C.  = 
2,507°F.  sufficient  gold  had  distilled  to  produce  a  gold 
mirror. 

The  high  temperature  researches  carried  out  by  Moissan 
with  the  aid  of  the  electric  furnace  are  detailed  in  his  book 
Le  Four  Electrique,  to  which  the  reader  is  referred  for 
particulars  of  his  experiments.  He  is  essentially  a  scien- 
tific enthusiast,  and  pursued  his  investigations  with  a  view 
of  adding  to  the  scientific  knowledge  of  the  day.  His 
work,  which  is  mainly  of  a  laboratory  and  experimental 
character,  has  nevertheless  been  instrumental  in  suggesting 
several  of  the  industrial  electric  furnace  processes  which 
are  in  operation  to-day. 

With  the  aid  of  furnaces  devised  by  himself,  Moissan 
has  succeeded  in  fusing,  distilling,  and  crystallizing  many 
of  the  most  refractory  substances,  among  which  may  be 
mentioned  magnesia,  lime,  platinum,  and  carbon. 

In  connexion  with  the  last-named  element  he  has  con- 
ducted extensive  investigations  into  the  properties  of  its 
allotropic  modifications,  and  last,  but  not  least,  has  actually 
succeeded  in  manufacturing  diamond. 

His  researches  in  the  preparation  of  carbides,  borides, 
and  silicides,  resulted  in  quite  a  quantity  of  hitherto  un- 
known compounds,  among  which  may  be  mentioned  the 
now  familiar  calcium  carbide  and  silicon  carbide  (car- 
borundum) of  commerce. 

Moissan  originally  described  the  carbides  of  calcium, 
strontium,  and  barium  as  opaque,  except  when  obtained 
in  very  thin  sheets. 

He   has   since   modified   this   description   in   accordance 

231 


ELECTRIC    FURNACES    AND 

with  the  results  of  later  experiments  (Comptes  Eendus, 
December  5,  1898).  He  ascribes  the  opacity  of  calcium 
carbide  to  impurities,  principally  iron,  which  are  present 
in  the  mass.  When  obtained  in  an  absolutely  pure 
state  it  is  as  transparent  as  lithium  carbide  or  sodium 
chloride. 

That  this  is  so  may  be  demonstrated  by  a  simple  ex- 
periment. A  mixture  of  metallic  calcium  and  amorphous 
carbon,  obtained  by  the  rapid  combustion  of  acetylene, 
is  heated  to  a  dull  red,  yielding  a  white  product,  pure 
calcium  carbide,  which,  under  the  microscope,  proves  to 
be  a  collection  of  transparent  crystals. 

In  this  connexion  Moissan  further  points  out  that,  under 
these  conditions,  the  heat  of  combination  between  the 
carbon  and  the  calcium  is  sufficient  to  fuse  the  carbide, 
a  result  never  yet  achieved  in  commercial  practice. 

The  reddish-brown  tint  of  commercial  carbide  may  be 
reproduced  in  this  pure  white  mass  by  heating  it  with  a 
small  quantity  of  iron. 

The  carbides  of  potassium,  K2C2,  and  lithium,  Li2C2 
may  also  be  obtained  in  transparent  crystalline  plates, 
whilst  aluminium  carbide  A14C3  sometimes  crystallizes 
in  transparent  plates,  having  a  yellowish  tinge. 

MM.  Moissan  and  Kouznetzow  have  succeeded  in  pre- 
paring, by  direct  reduction  in  the  electric  furnace,  a  double 
carbide  of  chromium  and  tungsten,  having  the  formula, 
W2C.3O3C2,  which  is  so  hard  as  to  scratch  glass,  topaz 
and  ruby,  though  not  diamond.  It  is  unattacked  by 
acids,  either  individually  or  mixed,  but  is  dissolved  by 
fused  chlorate  and  alkalies. 

Messrs.  Tucker  and  Moody  have  succeeded  in  producing 
the  borides  of  zirconium,  chromium,  tungsten,  and 
molybdenum,  by  heating  these  metals  in  conjunction  with 
borax,  in  the  electric  furnace.  The  current  required  was 
from  200  to  275  amperes.  Attempts  were  made  by  the 
same  experimenters  to  prepare  borides  of  copper  and 

232 


THEIR    INDUSTRIAL    APPLICATIONS 

bismuth  in  a  similar  manner,  but  were  not  attended  with 
success. 

Bolton  has  succeeded  in  bringing  about  a  direct  union 
between  carbon  and  chlorine  by  striking  an  arc  between 
two  carbon  electrodes  in  an  atmosphere  of  the  latter  gas. 

Hutton  has  conducted  a  series  of  experiments  on  the 
fusion  of  quartz,  and  the  results  of  his  efforts  were  em- 
bodied in  the  form  of  an  article  in  the  Electro-Chemist  and 
Metallurgist,  May,  1902. 

He  first  employed  an  open  arc  to  effect  the  fusion,  and 
found  that  reduction  took  place  in  the  immediate  neigh- 
bourhood of  the  arc,  giving  rise  to  a  black  stain  on  the 
surface  of  the  quartz,  which,  however,  disappeared  on 
holding  the  mass  away  from  the  centre  of  the  flame  for 
a  short  time. 

He  subsequently  continued  his  experiments  with  a  closed 
furnace,  using  one  of  the  Moissan  type,  modified  by  cutting 
openings  in  its  side  walls  to  permit  the  passage  of  a  carbon 
vessel  charged  with  quartz,  in  a  line  at  right  angles  to  the 
arc.  A  current  of  300  amperes  at  50  volts  was  employed, 
and  thick- walled  quartz  tubes,  having  an  internal  diameter 
or  bore  of  about  J  in.,  were  easily  cast  in  a  rough  carbon 
mould,  a  carbon  core  at  the  centre  securing  the  correct 
position  of  the  bore. 

The  charge  for  the  mould  consisted  of  broken  quartz, 
not  too  finely  powdered,  and  the  resultant  tubes  were 
easily  withdrawn  from  the  carbon  mould  and  freed  from 
the  cores.  They  were  not  quite  free  from  air-bubbles, 
but  were  improved  in  appearance  by  subsequent  re-heating 
under  the  arc,  the  tube  being  meanwhile  rotated. 

The  new  quartz  tubes  for  laboratory  research  at  high 
temperatures  have  considerably  extended  the  field  of 
investigation.  Metals  may  be  boiled  and  evaporated  in 
them  at  temperatures  up  to  1,200°C.=  2,192°F.,  and, 
with  care,  up  to  1,400°C.  =  2,552°F.,  even  in  a  high  vacuum, 
and  the  tubes  containing  metal  at  the  former  temperature 

233 


ELECTRIC    FURNACES    AND 

may  be  safely  removed  from  the  furnace,  cooled,  and 
replaced,  without  fear  of  breakage.  Using  an  electric 
furnace,  it  is  possible  to  regulate  the  temperature,  within 
two  or  three  degrees,  between  18°  and  1,400°C.  =  64° 
and  2,552°F.,  whilst  the  air-pump  connexions  to  the  tubes 
may  be  hermetically  sealed  with  wax  without  risk  of  melt- 
ing, although  within  a  few  inches  of  the  intense  heat. 


234 


THEIR    INDUSTRIAL   APPLICATIONS 


SECTION    XI 

TUBE  FURNACES 

Mr.  H.  N.  Potter,  of  New  York,  has  devoted  considerable 
attention  to  the  perfecting  of  a  series  of  tube  furnaces, 
in  which  the  hearth  takes  the  form  of  a  refractory  con- 
ducting tube,  through  the  walls  of  which  the  current  is 
passed  in  a  longitudinal  direction,  heating  them  in  its 
passage. 

There  are  several  difficulties  connected  with  the  efficient 
operation  of  this  type  of  furnace,  among  which  may  be 
mentioned — 

1.  The  attainment  of  an  even  heating  effect  in  all  parts 
of  the  tube. 

2.  Interchangeability    of    parts,     whereby    those    most 
subject  to  wear  are  rendered  easily  replaceable. 

3.  Satisfactory   terminal   connexions,   which   shall   allow 
for  the  necessary  expansion  and  contraction  of  the  tube 
itself. 

These  are  the  main  difficulties  which  Mr.  Potter  has 
realized,  and  set  himself  to  overcome,  and  we  will  now 
proceed  to  consider  the  various  forms  of  tubular  furnace 
construction  advocated  by  him,  and  the  manner  in  which 
they  severally  contribute  towards  the  desired  result. 

The  discovery  of  the  Nernst  principle  has,  as  already 
stated,  opened  up  another  promising  field  for  electric 
furnace  construction,  to  which  the  tubular  type  readily 
lends  itself ;  the  several  improvements  with  which  we 
shall  now  proceed  to  deal  are  equally  applicable  to  furnaces 
on  the  Nernst  principle,  and  to  the  older  forms  of  carbon 
tube. 

Equalization  of  Heating  Effect. — Mr.  Potter  suggests  three 

235 


f  ELECTRIC  ^FURNACES  AND 

distinct  forms  of  construction  for  the  tube,  with  a  view  to 
securing  a  uniform  distribution  of  heat  to  all  parts  of  the 
latter.  His  first  construction  consists  of  a  simple  tube, 
the  terminal  connexions  to  either  extremity  of  which  are 
subdivided.  Thus,  a  series  of  equidistant  points  to  the 
number  of  six,  or  upwards,  are  marked  off  around  the 
annular  surface  at  each  extremity  of  the  tube  ;  separate 
and  distinct  terminal  connexions  are  made  to  each  of  these 
points,  and  the  current  may  be  derived  from  a  transformer 
with  subdivided  secondary  winding,  the  number  of  sub- 
divisions being  equal  to  the  number  of  pairs  of  terminal 
points  to  the  furnace  tube. 

The  second  type  of  tube  to  secure  equal  heating  takes 
the  form  of  a  partially  divided  cylinder ;  longitudinal 
divisions  or  grooves,  spaced  at  equal  distances  apart, 
around  the  external  periphery  of  the  tube,  serve  to  con- 
centrate the  flow  of  current  along  definite  lines,  repre- 
sented by  the  intervening  sections  of  tube. 

The  third  form  of  construction  consists  in  a  total  longi- 
tudinal subdivision  of  the  tubular  walls  into  a  number 
of  similar  parts,  the  intervening  spaces  being  filled  in  with 
refractory  insulating  plates  after  the  manner  of  a  dynamo 
commutator. 

A  further  improved  construction  of  tube  furnace,  designed 
by  Mr.  Potter  with  a  view  to  the  additional  strengthening 
of  parts,  prevention  of  distortion  of  the  tube  under  the 
effects  of  heat,  and  conservation  of  the  heat  produced, 
is  shown  in  Fig.  52.  It  comprises  a  carbon  tube  C, 
which  may  or  may  not  be  provided  with  an  interior  re- 
movable lining  T,  also  tubular ;  carbon  terminal  discs 
D  D,  and  a  series  of  annular  ribs  r  r  of  the  same  material, 
which  are  slipped  over  the  tube,  and  serve  as  an  additional 
support  thereto.  The  spaces  between  the  ribs  r  r  are 
filled  in  with  magnesia  m,  covered  by  a  layer  of  asbestos, 
and  the  whole  is  enclosed  in  a  glazed  earthenware  jacket  J. 
As  may  be  readily  imagined,  this  provides  a  very  rigid 

236 


THEIR    INDUSTRIAL    APPLICATIONS 


FIG.  52. 


construction,  whilst  the 
loss  of  heat,  resulting 
from  radiation,  is  com- 
paratively small. 

Terminal  Connexion 
and  Mounting  of  Tubu- 
lar Furnaces.  —  Mr.  Pot- 
ter has  also  tackled  this 
problem,  and  the  resul- 

tant design  is  that  of  a  form  of  terminal  connexion  and  mount- 
ing for  tubular  furnaces,  which  enables  the  latter  to  be  placed 
in  any  position,  and  allows  for  the  necessary  expansion 
without  resultant  disturbance  of  the  electrical  connexions. 
It  is  represented  in  Fig.  53,  where  C  is  the  carbon 
tube,  as  before  ;  D  D  terminal  discs,  or  rings  of  the  same 
material,  the  outer  surfaces  of  which  are  double-tapered 
as  shown,  to  form  a  seating  for  the  metal  clamping  rings 
r  r,  held  together,  and  in  good  electrical  contact  with  the 
carbon,  by  the  bolts  &  &  ;  A  A  are  sheet  metal  diaphragms, 
through  which  the  bolts  6  also  pass,  thus  securing  them 
to  the  terminal  rings  of  the  tube.  The  outer  edges  of  the 
diaphragms  are  clamped  between  metal  end  plates  p  p, 

and  the  flanged 
extremities  of 
an  outer  casing 
B,  suitable  in- 
sulation being 
inserted  at  the 
joint.  The 
flexibility  of  the 
metallic  dia- 
phragms A  per- 
mits^the  neces- 
sary expansion 
of  the  tube 
under  heat, 
237 


-  53- 


ELECTRIC    FURNACES    AND 

whilst  the  actual  electrical  connexions  from  the  source  of 
energy  are  made  to  the  end  plates  p,  and  are  thus  ren- 
dered independent  of  any  movement  in  the  tube  itself. 

Another  departure  in  tube  furnace  construction  consists 
in  the  provision  of  an  additional  source  of  heat  within  the 
tube  itself  ;  this  takes  the  form  of  an  arc  between  two 
carbon  electrodes,  the  position  of  which  is  adjustable 
longitudinally  along  the  axis  of  the  tube,  so  as  to  bring 
the  arc  to  any  desired  point. 

A  revolving  tube  furnace,  boasting  the  above  com- 
bination of  arc  and  resistance  principles,  is  represented 
in  Fig.  54.  The  tube  proper  consists  of  separate  graphite 
sections  g  g,  pieced  together  to  form  a  complete  cylinder, 
and  surrounded  by  an  insulating  jacket  j,  which  latter 
is,  in  turn,  enclosed  in  a  sheet  metal  casing  c.  Around 
the  periphery  of  the  casing  are  arranged  two  annular  metal 


FIG.  54. 

bearing  pieces  b  b,  which  serve  as  journals  to  the  tube, 
being  mounted  on  rollers  r  r.  The  necessary  motive  power 
to  rotate  the  furnace  is  supplied  through  a  pulley  P,  also 
mounted  on  the  outer  casing.  E  E  are  fixed  end  pieces, 
or  covers,  lined  with  graphite  blocks  a  a  which  make 
rubbing  contact  with  the  tube  sections  g,  outer  insulation 
i,  and  metallic  casing  ra  m.  These  latter  form  the  ter- 
minal attachments  for  the  resistance  portion  of  the  furnace. 
The  arc  electrodes  A,  A2  are  introduced  through  in- 

238 


THEIR    INDUSTRIAL    APPLICATIONS 

sulating  bushes  in  the  centre  of  the  end  covers,  E  E  and, 
as  stated  above,  are  adjustable  as  regards  their  axial  position 
in  the  furnace.  I  and  0  are  inlet  and  outlet  orifices  re- 
spectively for  the  introduction  of  the  raw  material,  and 
withdrawal  of  the  product.  They  penetrate  the  stationary 
end  covers,  as  shown,  and,  the  tube  being  preferably 
mounted  at  an  angle,  the  process  is  rendered  continuous, 
the  charge  passing  through  by  virtue  of  rotation  and 
gravitation  from  one  end  of  the  tube  to  the  other. 

Mr.  Potter's  design  for  a  tube  furnace  on  the  Nernst 
principle,  especially  adapted  to  the  baking  of  "  glowers  " 
for  Nernst  lamps,  comprises  a  simple  tube,  formed  from 
a  mixture  of  the  electrolytic  oxides  of  magnesia,  or  zirconia, 
and  yttria,  fitted  with  terminal  connexions,  and  enclosed 
in,  and  strengthened  by  an  encircling  jacket,  consisting 
of  one  only  of  the  oxides  named  above. 

Over  this  again  is  wound  the  heater  coil,  a  layer  of  mica 
being  interposed  between  them.  The  actual  heat  is 
developed,  once  the  action  is  started  by  the  coil,  in  the 
inner  tube  of  mixed  oxides,  the  outer  jacket  remaining, 
to  all  intents  and  purposes,  a  non-conductor,  whilst,  at 
the  same  time,  its  chemical  similarity  to  the  furnace  tube 
proper  prevents  any  detrimental  action  from  taking  place 
between  them. 

This  notion  of  a  single  oxide  for  a  protective  and  sup- 
porting jacket  is  one  of  the  essentials  of  Potter's  patent, 
any  other  refractory  substance  being  unsuitable  on  account 
either  of  its  electrolytic  properties  when  heated,  or  of  its 
tendency  to  unite  chemically  with  the  substance  of  the 
furnace  tube  proper. 

A  resistance  tube  furnace  on  the  Nernst  principle,  devised 
by  Drs.  Nernst  and  Glaser,  is  illustrated  in  Fig.  55.  The 
resistance  heater  is  in  the  form  of  a  hollow  cylinder,  or 
tube  R,  composed  of  the  usual  electrolytic  oxides,  pre- 
ferably a  mixture  of  magnesia,  with  traces  of  calcium 
carbonate,  silica  or  kaolin,  and  alumina.  It  is,  like  one 

239 


ELECTRIC    FURNACES    AND 


of  the  tube  furnaces  already  described,  enclosed  in  a  second 
cylinder  C,  of  loose  oxides,  held  in  place  by  an  outer  casing 
J,  which  serves  to  retain  the  heat.  The  electrodes  are 
an  especial  feature  of  the  construction,  and  consist  of 
oxide  of  iron  F  packed  closely  round  the  two  ends  of  the 
tube  in  annular  form,  which  latter  is  preserved,  and  the 
oxide  held  in  position  by  iron  hoops  /,  secured  and  drawn 

together  by  bolts  and  nuts. 
A  refractory  lid  L  is  pro- 
vided, and  the  furnace  stands 
on  a  base  B.  The  raw 
material  to  be  treated  therein 
may  either  be  placed  directly 
in  the  tube,  in  which  case  it 
is  lined  interiorly  with  mag- 
nesia, or  in  a  separate  cruc- 
ible c,  supported  by  a  re- 
movable portion  of  the  base. 
The  action  of  the  furnace  is 
started  by  a  preliminary  heat- 
ing of  the  tube,  either  with 

a  gas  flame,  as  in  torch-actuated  Nernst  lamps,  or  by  a 
carbon  resistance  rod  introduced  axially  through  the  tube 
and  heated  by  the  passage  of  the  current. 

The  Eddy  tube  furnace,  invented  and  patented  by  A. 
H.  Eddy,  was  specially  designed  for  the  fusion  of  enamels 
upon  earthen  and  metallic  ware,  a  process  calling  for  ex- 
tremely fine  temperature  regulation,  and  freedom  from 
ash  and  combustion  vapours.  It  consists  of  a  series  of 
tubes,  composed  of  such  electrolytic  oxides  as  conduct 
when  heated.  Axially  within  these  tubes,  but  not  in 
electrical  contact  with  their  inner  walls,  are  arranged 
carbon  rods,  which,  heated  by  the  current,  serve  for  the 
preliminary  heating  of  the  tubes  themselves. 

The  combinations  of  tubes  and  rods  are  mounted  in 
batches,  of  varying  number,  between  water-cooled  ter- 

240 


FIG.  55. 


THEIR    INDUSTRIAL    APPLICATIONS 

minal  blocks.  The  furnace  itself  is  constituted  by  arranging 
a  number  of  these  combinations  transversely  across  a  long, 
narrow  hearth,  over  which,  and  beneath  the  tubes,  are 
packed  the  articles  to  be  heated. 

Varying  gradations  of  temperature  at  different  points 
along  the  length  of  the  furnace  are  secured  by  connecting 
the  several  sections  in  series,  their  respective  heating 
capacities  being  regulated  by  the  number  of  tubes  com- 
prising them. 

The  initial  heating  of  the  tubes  is  effected  by  the  passage  of 
a  current  through  the  carbon  rods,  thus  heating  the  tubes, 
which,  in  turn,  become  conductors,  and  shunt  a  portion 
of  the  current.  The  rods  may  subsequently  be  entirely 
withdrawn,  when  the  maximum  heating  effect  is  obtained 
within  and  around  the  substance  of  the  tubes  themselves. 

What  is  known  as  an  electric  combustion  furnace,  being 
a  combination  of  an  ordinary  combustion  tube,  with 
electrical  means  for  starting  and  maintaining  high  degrees 
of  temperature  therein,  has  been  designed  by  Mr.  W.  M. 
Carr.  It  consists  of  a  combustion  tube  proper,  with  copper 
gauze  at  'one  extremity  and  granular  oxide  of  copper 
between  perforated  platinum  discs  at  the  other,  surrounded 
by  an  electrical  .portion,  which  serves  to  produce  and 
maintain  the  necessary  heat. 

It  comprises  a  porcelain  cylinder  surrounding  the  com- 
bustion tube,  and  having  three  heating  coils  wound  upon 
it,  one  at  either  extremity,  and  the  other  at  the  centre. 
A  heat  conserving  jacket  of  magnesia  encloses  the  whole 
apparatus.  The  mode  of  operation  is  as  follows :  The 
material  to  be  treated  is  placed  in  a  platinum  boat  at  the 
centre  of  the  inner  combustion  tube  ;  by  means  of  inde- 
pendent switching  arrangements,  a  current  is  first  passed 
through  the  two  end  coils  in  series,  and  raises  the  tube 
and  its  contents  to  the  required  temperature,  the  latter 
being  subsequently  maintained,  so  long  as  desired,  by  all 
three  coils  connected  in  series. 

241  R 


ELECTRIC    FURNACES    AND 

The  usual  means  are  provided  for  the  introduction  of 
oxygen  gas  to,  and  the  withdrawal  of  the  products  of  com- 
bustion from,  the  tube. 

A  convenient  form  of  laboratory  resistance  furnace, 
exhibited  by  Mr.  Otto  T.  Louis,  at  the  Conversazione  of 
the  American  Institute  of  Electrical  Engineers,  in  1901, 
has  a  tubular  construction,  and  consists  of  several  terra 
cotta  cylinders,  each  about  two  inches  in  diameter,  and 
half  an  inch  in  thickness.  Around  these  are  wound  the 
heating  resistance  spirals,  consisting  of  platinum  wire, 
about  No.  23  S.W.G.  Switching  facilities  are  provided, 
whereby  the  wire,  which  is  arranged  in  four  distinct  circuits, 
can  be  connected  in  series  to  start  the  furnace,  and  then, 
as  the  resistance  rises  with  increasing  temperature,  in 
parallel  to  maintain  the  heat. 

A  so-called  electric  oven,  or  small  resistance  furnace 
of  the  tube  type,  is  employed  in  the  German  Reichsanstalt 
for  the  calibration  of  thermo-couples  used  in  high  tem- 
perature thermometry. 

It  consists  of  four  concentric  porcelain  tubes,  the  outer 
being  glazed,  and  jacketed  with  asbestos.  The  inner 
tubes  are  composed  of  a  very  refractory  material,  devised 
by  Hecht.  The  second  tube  serves  as  a  mandrel  or  base 
for  the  heating  resistance,  which,  in  the  form  of  wire, 
is  wound  upon  it.  For  procuring  temperatures  up  to 
1,400°C.=  2,552°F.,  a  pure  nickel  wire,  having  a  diameter 
of  2  m.m.,  is  used,  and  is  protected  by  a  layer  of  fire-clay 
paste  laid  on  so  as  to  embed  the  turns.  For  higher  tem- 
peratures a  platino-iridium  wire  is  used,  which  increases 
the  range  to  1,600°C.=  2,912°F.  Above  this  the  wire 
fuses  into  the  porcelain. 

Temperature  regulation  is  effected  with  a  great  degree 
of  accuracy  by  means  of  an  adjustable  rheostat,  the  sliding 
contact  of  which  moves  over  and  makes  contact  with  a 
constantan  band. 

The  thermo-couples  are  calibrated  in  sets  by  a  com- 

242 


THEIR    INDUSTRIAL    APPLICATIONS 

pensation  method,  being  mounted,  for  the  purpose,  in  small 
circularly  gapped  sockets  of  platino-iridium.  The  errors 
do  not  exceed  O'l  per  cent. 

The  power  consumed  in  the  furnace  is  low,  being  sixty 
watts  for  a  temperature  of  200°C.  =  392°F.,  and  rising 
to  1,540  watts  for  1,3000C.=  2,372°F. 

Observations  on  the  melting-point  of  the  element  man- 
ganese were  carried  out  at  the  beginning  of  1902  by  Heraeus, 
of  Hanau,  in  a  specially  constructed  furnace  of  the  tube 
pattern,  devised  by  this  firm.  The  furnace  consisted  of 
a  porcelain  tube,  16  m.m.  in  diameter  and  30  c.m.  long. 
Around  a  portion  of  this  tube  is  wound,  spirally,  the  heating 
resistance,  in  the  shape  of  a  strip  of  platinum  foil. 

Efficient  and  gradual  regulation  of  the  temperature  is 
secured  by  means  of  an  adjustable  resistance  connected 
in  series  with  the  foil.  With  this  arrangement  a  tempera- 
ture of  1,400°C.=  2,552°F.  could  be  attained  within  three 
minutes  of  switching  on  the  current,  whilst  the  maximum 
temperature  available  was  1,600°C.=  2,912°F. 

Addressing  a  meeting  of  the  German  Electro-Chemical 
Society  in  the  same  year,  Dr.  Haagn,  chemist  to  the  firm 
of  Heraeus,  expatiated  upon  the  advantages  of  this  new 
form  of  laboratory  tube  furnace  construction. 

The  heating  resistances  in  previous  furnaces  of  a  similar 
type  have  been  wire,  and  Dr.  Haagn  estimates  the  weight 
of  platinum  required  when  foil  is  used  to  be  only  T^  to 
-^Q  that  necessary  in  a  wire  resistance. 

Referring  to  the  tubes,  the  same  authority  stated  that 
glass  or  porcelain  was  preferable  to  magnesia,  as  a  safeguard 
against  electrolytic  dissociation  and  consequent  injury 
to  the  platinum  heater  in  the  neighbourhood  of  the  cathode. 
Above  a  temperature  of  1,500°C.  =  2,732°F.,  the  same 
effect  is  observed  even  with  tubes  constructed  of  the  best 
Berlin  porcelain,  but,  with  specially  manufactured  tubes, 
a  temperature  as  high  as  1,700°C.— 3,092°F.  has  been 
maintained  for  a  short  period  without  injury. 

243 


ELECTRIC    FURNACES    AND 

Dr.  Haagn  recommends  this  type  of  furnace  for  use  in 
chemical  and  physical  laboratories,  and  points  out  its  appli- 
cability to  such  operations  as  ash  determinations,  organic 
combustion  analysis,  the  direct  determination  of  carbon 
in  steel  by  the  Lorenz  method,  etc. 

A  subdivision  of  the  special  heating  resistance,  with 
suitable  provision  for  separate  terminal  connexions  to  each 
section,  largely  increases  the  range  of  utility  of  this  furnace, 
in  that  it  enables  the  heating  of  various  sections  of  the 
tubular  hearth  to  be  carried  out  independently  or  together, 
at  the  will  of  the  operator. 

The  platinum  foil  employed  in  the  Heraeus  tube  furnace 
is  0*007  m.m.  thick.  The  furnace  is  easily  regulated  by 
means  of  a  series  resistance.  These  furnaces  can  be  made 
for  any  voltage  up  to  220,  but,  for  very  high  temperatures, 
low  voltages  are  said  to  answer  best. 

A  modification  of  the  Heraeus  furnace,  for  heating  porce- 
lain tubes,  etc.,  was  described  in  the  Journal  de  Chimie 
Physique  (1903,  I.  177)  by  M.  A.  Guntz.  The  foundation 
consists  of  a  tube  of  refractory  earths,  several  millimetres 
thick  ;  60  m.m.  longer,  and  with  an  internal  diameter  or  bore, 
from  four  to  five  m.m.  larger  than  the  external  diameter 
of  the  tube  or  article  to  be  heated.  This  tube  is  given  several 
coats  of  a  paste  made  up  of  magnesia  and  alumina,  mixed 
either  in  the  proportion  of  equal  molecules  of  the  two 
oxides,  or  eight  molecules,  of  magnesia  to  one  of  alumina, 
to  which  some  gelatinous  alumina,  or  a  weak  solution  of 
aluminium  acetate,  is  added  as  a  binding  material. 

An  alternative  paste  is  made  up  of  one  part  strongly 
ignited  alumina  ;  one  part  of  alumina  obtained  by  incom- 
plete calcination  of  ammonium  alum,  and  one  part  calcium 
aluminate,  prepared  by  heating  to  redness,  equal  weights 
of  alumina  and  pure  chalk.  No  appreciable  trace  of  silica 
should  be  present  in  the  ingredients. 

The  layers  of  paste  are  dried  naturally  in  air,  as  the 
result  of  which,  they  adhere  well.  The  dimensions  of  the 

244 


THEIR    INDUSTRIAL    APPLICATIONS 

platinum  wire  required  to  produce  a  pre-determined  heating 
effect  are  then  calculated  from  the  equation  — 


Where  E  represents  the  maximum  available  voltage, 
„      C         „  „       current, 

„      S         „  „       section  of  the  wire, 

,,      1         ,,  ,,       length  of  the  wire, 

and      R         „  ,,       resistivity  of  one  metre  of  plati- 

num wire,  having  a  cross-section  of  one  square  millimetre, 
a  quantity  which  requires  to  be  ascertained  for  the  particular 
sample  available. 

Having  thus  found  the  length  and  diameter,  a  simple 
calculation  will  serve  to  determine  the  number  of  turns 
to  be  coiled  on  the  tube  ;  suffice  it  to  say  that,  unless  a 
specially  rapid  heating  effect  be  desired,  neighbouring 
turns  should  not  be  less  than  5  m.m.  apart.  Having  deter- 
mined the  number  and  pitch  of  the  spirals,  a  suitable 
thread  or  groove,  about  '5  m.m.  deep,  is  chased  in  the  pre- 
pared coating  of  the  tube.  The  platinum  wire  is  laid  in 
place  in  the  groove  thus  prepared  for  its  reception,  the  two 
end  turns  being  double,  and  tied,  or  otherwise  secured  in 
place. 

A  number  of  coats  of  the  original  paste  are  then  applied 
over  all,  to  a  thickness  of  four  or  five  millimetres,  the  whole 
being  then  encased  in  a  sheet  of  asbestos.  A  weak  current 
is  first  passed  through  the  spiral,  warming  it  sufficiently 
to  drive  the  moisture  out  of  the  paste,  which  should  remain 
firm.  In  the  event  of  cracking,  the  openings  mus.t  be 
filled  in  with  paste.  A  final  jacket  of  asbestos  sheet,  on 
which  are  mounted  suitable  terminals,  completes  the  con- 
struction. 


245 


ELECTRIC    FURNACES    AND 


SECTION    XII 

TERMINAL  CONNEXIONS  AND  ELECTRODES 

The  terminal  connexions  to  the  electrodes  of  electric 
furnaces  have  long  been  a  source  of  trouble  to  the  operator, 
and  an  object  for  the  application  of  the  inventor's  genius 
and  forethought.  There  are  several  important  points  to 
be  considered  in  the  design  of  an  efficient  terminal  connexion 
to  carry  the  large  currents  met  with  in  electric  furnace 
work. 

(1)  They  must  possess  a  certain  amount  of  flexibility 
in  order  to  allow  of  the  necessary  adjustments. 

(2)  They  must  establish  good  electrical  connexion  with 
the  electrode  on  the  one  hand,  and  with  the  conducting 
cables  on  the  other. 

(3)  They    must    not    become    unduly  heated  when  the 
furnace  is  at  work. 

(4)  They  must  not  be  of  such  a  nature  as  to  radiate  a 
considerable    percentage   of    heat   and    thereby  lead  to   a 
serious  reduction  in  the  efficiency  of  the  furnace. 

Many  and  varied  are  the  designs  which  have  been  evolved 
from  time  to  time,  with  a  view  to  meeting  all  these  require- 
ments in  one  and  the  same  device,  and,  although  some  con- 
siderable improvement  in  the  means  for  transmitting  the 
current  to  the  furnace  electrodes  has  undoubtedly  been 
effected  during  the  last  few  years,  there  is  still  a  good  deal 
of  room  for  more,  and  those  interested  in  furnace  industries 
might  do  worse  than  turn  their  attention  at  spare  moments 
to  the  improvement  of  this  important  accessory,  which,  if 
badly  designed,  is  quite  capable  of  wasting  several  horse- 
power in  a  plant  of  moderate  capacity. 

246 


THEIR    INDUSTRIAL    APPLICATIONS 

One  of  the  earlier  Cowles'  furnaces  was  provided  with  a 
somewhat  novel  terminal  arrangement,  which  has  since 
fallen  into  disuse.  It  consisted  of  a  species  of  metallic 
gland  or  stuffing  box,  filled  with  copper  shot,  through  the 
centre  of  which  passed  the  electrodes.  These  latter  set 
up  a  good  rubbing  contact  with  the  shot,  and,  through  them, 
with  the  metallic  sleeves  ;  a  contact  which  was,  in  fact, 
improved  by  use,  in  that  the  motion  of  the  electrodes,  in 
feeding  them  forward  into  the  furnace,  revolved  the  shot,  and 
brought  fresh  clean  surfaces  into  contact  with  one  another. 
In  furnaces  having  a  suspended  electrode  it  is  frequently 
arranged  that  the  support  for  this  latter  shall  also  serve 
to  convey  the  current  to  it.  This  construction  answers 
very  well  for  furnaces  of  moderate  size,  but  is  not  suitable 
for  larger  types,  in  that  the  two  governing  features,  con- 
ductivity and  strength,  do  not  increase  in  like  proportion. 
A  form  of  terminal  connexion,  devised  with  a  view  to 
overcoming  this  difficulty,  has  been  patented  by  Fausto 
Morani,  his  apparatus  consisting  of  a  supporting  frame  for 
the  electrode,  which  is  separate  and  distinct  from  the  electrical 
connexion  thereto.  Both  attachments  are  furnished  with 
means  for  the  circulation  of  water  for  cooling  purposes. 

E.  G.  Acheson,  one  of  the  recognized  leaders  in  the  field 
of  electric  furnace  work,  has  also  attacked  the  problem, 
his  latest  design  of  terminal  for  resistance  furnaces  being 
capable  of  dealing  efficiently  with  so  large  a  current  as 
37,500  amperes,  and  this  with  a  total  cross-section  of  only 
1,152  square  inches,  representing  an  approximate  current 
density  of  32*5  amperes  to  the  square  inch. 

A  transverse  section  of  the  terminal  is  shown  in  Fig.  56. 
It  comprises  72  square  blocks  C  C  of  graphitized  carbon, 
each  having  a  cross-sectional  area  of  16  square  inches. 
These  are  placed  in  block  form,  as  close  together  as  possible, 
and  end  on  to  a  copper  plate  A,  to  which  they  are  clamped 
by  studs  S,  and  nuts  N.  One  of  the  attachments  is  shown 
in  section  in  the  figure,  and  it  will  be  seen  that  the  portion 

247 


ELECTRIC    FURNACES    AND 


FIG.  56. 


of   the  stud  s,  which  screws    into  the   carbon  block  C,  is 

larger  in  diameter  than 
the  portion  projecting 
through  the  copper 
plate,  thus  furnishing  a 
shoulder  which  butts 
up  against  a  raised  por- 
tion of  the  latter,  and 
takes  all  strain,  arising 
out  of  the  clamping,  off 
the  carbon  itself. 

The  copper  plate  A 
constitutes  one  wall 
of  a  flat  water  tank, 

he  remaining  wall  D  being  of  sheet  metal.  The  sides 
and  bottom  of  the  tank  are  formed  of  flanged  pieces 
E,  into  circular  openings  p  p,  in  which,  a  series  of  cable 
ends,  forming  the  main  electrical  connexions  to  the  elec- 
trode, are  sweated.  A  tank  T,  in  which  a  constant  level 
of  water  is  maintained,  communicates  with  the  flat  tank 
or  base  of  the  electrode  by  a  pipe  t,  and  a  constant  circula- 
tion of  cooling  water  is  thus  secured. 

The  following  are  among  the  difficulties  experienced 
in  designing  an  efficient  and  convenient  form  of  terminal 
connexion  for  electric  furnaces  employing  carbon  electrodes. 
In  the  first  place,  metal  has  a  higher  expansion  co-efficient 
than  carbon  ;  consequently  the  heat  conducted  from  the 
furnace  itself,  together  with  the  hot  gases  produced,  and 
which  tend  to  make  their  escape,  among  other  places,  at  the 
point  of  entry  of  the  electrodes  through  the  furnace  walls, 
both  tend  to  expand  the  metal  portions  to  a  greater  extent 
than  the  corresponding  parts  of  the  carbon  electrodes. 
A  small  air-gap  is  consequently  created  between  the  two, 
and  the  electrical  resistance  at  the  surfaces  of  contact 
rises  very  rapidly.  This,  in  itself,  sets  up  a  further  heating 
effect,  which  may,  in  extreme  cases,  be  heightened  by  arcing, 

248 


THEIR    INDUSTRIAL    APPLICATIONS 

set  up  between  two  widely  separated  points,  which  ulti- 
mately tends  to  destroy  the  connexion  entirely  from  an 
electrical  point  of  view. 

Chavarria  Contardo's  patent  form  of  terminal  connexion 
for  electric  furnaces  is  both  ingenious  and  convenient,  in 
that  it  permits  the  necessary  sliding  movement  of  the  car- 
bons, to  compensate  for  combustion  and  wear,  without  dis- 
turbing the  electrical  connexions  thereto. 

Cylindrical  carbons  are  employed,  and  they  slide  in 
water- jacketed  sleeves,  let  into  the  wall  of  the  furnace 
structure.  Electrical  connexion  with  the  sleeve  is  rendered 
secure,  and  a  low  resistance  path  provided  for  the  current, 
by  prolongations  of  the  metal  sleeves,  consisting  of  a  series 
of  bronze  segments,  which  encircle  the  carbon  electrode, 
and  are  maintained  in  intimate  contact  with  it  by  means  of 
set  screws.  A  thin  packing  of  sheet  copper  is  usually  inter- 
posed between  the  bronze  segments  and  the  surface  of  the 
carbon,  for  the  better  protection  of  the  former. 

Some  saving  in  space,  and  length  of  active  circuit,  may 
be  effected  by  employing  hollow  segments,  which  are  them- 
selves water-cooled,  thus  avoiding  the  necessity  for  the 
complete  metal  sleeve  alluded  to  above. 

The  connecting  cable  is  either  in  multiple,  or,  if  in  single 
form,  is  split  up  into  a  series  of  strands  corresponding  with 
the  number  of  bronze  segments,  one  such  strand  or  cable 
being  connected  to  each  segment  by  a  suitable  mechanical 
joint,  thus  ensuring  an  even  distribution  of  the  current 
through  the  mass  of  the  electrode. 

This  construction  not  only  permits,  as  already  stated, 
a  sliding  feed  adjustment  of  the  electrodes,  but  also  a  con- 
stant feed,  even  when  a  length  of  carbon  becomes  too  short 
to  be  of  any  further  use  by  itself.  The  procedure  then 
consists  in  making  a  joint  outside  the  furnace,  between  it 
and  the  new  electrode  and  rendering  the  same  secure  by  a 
species  of  graphitic  cement. 

The  Cowles'  form  of  terminal  connexion  for  open  furnaces 

249 


ELECTRIC   FURNACES    AND 

consists  in  a  metal  socket  for  the  reception  of  the  carbon 
electrode.  A  water-cooling  jacket  is  arranged  in  close 
proximity  to  the  metal  socket,  and  an  inlet  pipe  is  fitted 
in  such  a  position  that  the  ingoing  water  strikes  against 
that  wall  of  the  jacket  which  adjoins  the  electrode  socket. 

An  outlet  is  also  provided  so  that  a  constant  circulation 
may  be  maintained. 

A  form  of  water-cooled  terminal  connexion,  designed  by 
O.  Imray,  is  adapted  to  electrodes  of  the  suspended  type. 
The  carbon  block  forming  the  electrode  is  suspended  from  a 
species  of  metal  cross-head,  above,  by  yoke  pieces,  shaped 
to  suit  the  block,  and  secured  to  the  supporting  cross-head 
by  bolts  and  nuts.  The  length  of  the  yoke  pieces  is  such 
that  the  cross-head  and  its  attached  parts  are  sufficiently 
removed  from  the  heat-zone  which  surrounds  the  upper 
part  of  the  carbon  electrode. 

Electrical  connexion  with  the  carbon  block  is  secured  by 
a  metal  capping,  which  either  butts  up  flat  against  its  upper 
extremity,  or  is  shaped  so  as  to  encircle  the  block  for  a 
short  distance  down.  This  capping  is  connected  with  the 
cross-head  by  a  central  metal  tube,  and  is  water-jacketed 
as  regards  its  surface  of  contact  with  the  carbon.  The 
upper  end  of  the  tube  is  jointed  to  the  main  conductor, 
whilst  axially  through  its  centre  runs  a  second  smaller  tube 
or  inlet  for  the  water  supply,  which  it  delivers,  as  already 
stated,  just  above  the  metallic  wall  which  is  in  contact  with 
the  carbon.  Openings  or  outlets  for  the  water  are  pro- 
vided in  the  outer  tube,  and  provision  is  made  for  a  com- 
plete circulatory  system,  whereby  the  yoke  pieces  themselves 
are  also  kept  cool. 

In  conjunction  with  this  patent  is  described  a  special 
form  of  outlet  for  molten  furnace  products.  Instead  of 
the  usual  tapping  hole,  with  its  attendant  drawbacks, 
slits  are  made  in  the  wall  of  the  furnace,  and  lined,  for  pro- 
tection, with  steel,  or  equally  suitable  metal,  which  is,  in 
turn,  water- jacketed. 

250 


THEIR    INDUSTRIAL    APPLICATIONS 

The  form  of  water-cooled  terminal  construction  originally 
adopted  for  the  Pictet  carbide  furnaces  at  Ingleton.  is  shown 
in  Fig.  57.  The  main  cable  M,  consisting  of  stranded 
No.  19  B.W.G.  copper  wire,  made  up  to  a  cross-section 
equal  to  three  square  inches  of  solid  copper,  is  compressed 
into  rectangular  form,  with  dimensions,  2J  by  2  in.,  and 
sweated  into  the  metal  socket  S,  which  is  water- jacketed 
as  shown.  The  square  extremity  of  the  carbon  electrode 
C,  6  by  6  in.,  is  socketed  into  the  other  extremity  of  the 
terminal,  which  is  mounted  on  a  travelling  carriage  A, 
moved  along  the 
slide  B,  as  occasion 
requires,  by  means 
of  a  screw  and  hand- 
wheel  W.  2,000 
amperes  were  effect- 
ually dealt  with  by 
this  form  of  terminal 
construction. 

Electrodes. — As  may  be  readily  imagined,  the  consump- 
tion of  electrodes  in  the  electric  furnace,  especially  where 
such  furnaces  are  worked  on  an  extensive  scale,  as  in  carbide 
manufacture,  is  by  no  means  inconsiderable. 

Several  firms  have,  in  consequence,  taken  up  the  manu- 
facture of  electrodes  for  use  in  their  own  furnaces.  Among 
these  may  be  mentioned  the  Societe  des  Carbures  Metal- 
liques,  which  owns  carbide  factories  situated  at  Notre  Dame 
de  Briancon,  Le  Castelet,  Bellegarde,  and  Berga.  The 
electrode  factory  is  situated  at  the  first  named,  and  the 
following  essential  features  of  the  manufacturing  process 
are  extracted  from  an  article  on  the  subject  by  M.  G.  Strauss, 
which  appeared  in  the  Revue  General  de  Chimie  Pure  et 
Applique  in  1901. 

The  raw  materials  are  retort  carbon,  petroleum  coke, 
and  coal  tar.  The  first  named  is  obtained  in  varying 
qualities,  and  calls  for  thorough  mixing  to  ensure  homogeneity 

251 


ELECTRIC    FURNACES    AND 

in  the  finished  product.  The  second,  petroleum  coke,  is  a 
porous  residue,  produced  in  the  distillation  of  crude  petro- 
leum. It  is  employed  specially  in  the  manufacture  of  very 
hard  and  dense  electrodes  such  as  are  used  in  electrolytic 
furnaces  with  fused  electrolytes,  and  is  very  pure.  The 
coal  tar,  used  as  a  binding  material,  is  either  produced 
in  process  of  refining  ammonia,  from  which  it  distils  over 
at  a  temperature  of  from  240°  to  330°F.  =  115°  to  166°C., 
or  it  may  take  the  form  of  a  mixture,  artificially  prepared, 
by  dissolving  pitch  at  steam  heat  in  a  heavy  tar  oil. 

The  process  itself  is  briefly  as  follows.  The  carbon  or 
coke,  as  the  case  may  be,  is  first  crushed  in  special  machinery, 
and  subsequently  sieved  into  powders  of  varying  degrees 
of  comminution,  their  classification  and  ultimate  use 
depending  upon  the  size  of  electrode  to  be  made  from 
them.  A  quantity  of  powder  of  the  required  grade  is 
then  selected  and  mixed  with  the  requisite  quantity  of 
coal  tar,  in  steam-jacketed  vessels,  after  which  the  mixture 
is  ground  under  heavy  edge  runners.  From  the  grinding 
process  it  emerges  as  a  thin,  flat,  plastic  cake,  ready  for 
compressing  and  moulding  into  shape.  To  this  end,  it  is 
formed,  by  hydraulic  pressure,  into  "  cartridges,"  or  ingots, 
which  may  weigh  anything  from  180  kgs.  to  a  ton,  according 
to  the  size  of  electrode  required.  The  latter  are  finally 
shaped  by  extrusion  from  a  die  under  enormous  hydraulic 
pressure,  amounting  to  as  much  as  2,000  tons  for  the  larger 
sizes. 

All  that  remains  before  the  electrodes  are  finally  ready 
for  use  in  the  furnaces,  is  to  stove  them,  a  process  carried 
out  in  a  Siemens  regenerative  furnace,  worked  continuously, 
the  electrodes  being  packed  for  the  purpose  in  muffles,  and 
the  interstices  filled  in  with  carbon  dust.  This  final  stoving 
occupies  a  period  of  several  days. 

To  ensure  a  satisfactory  product,  periodical  tests  for 
electrical  conductivity  are  made,  by  fastening  a  sample  of  the 
electrode  in  a  vertical  position  in  a  metal  mould.  Molten 

252 


THEIR    INDUSTRIAL    APPLICATIONS 

lead  is  then  poured  in  at  either  end  to  establish  electrical 
contact  with  the  carbon  surfaces,  and  holes,  drilled  in  the 
two  lead  castings,  at  a  certain  pre-determined  distance 
apart,  serve  as  mercury  cups  for  terminal  connexion  to  the 
testing  apparatus,  which  takes  the  form  of  a  Thomson  low 
resistance  bridge. 

The  conductivity  is  an  extremely  variable  quantity, 
depending  in  turn  upon  the  nature  of  the  raw  materials 
used,  and  upon  each  and  every  stage  of  the  manufacturing 
process. 

Current  density  and  temperature  have  a  most  important 
bearing  upon  the  life  of  electrodes,  more  particularly  anodes, 
in  an  electrolytic  bath.  Graphitized  carbon  is  less  susceptible 
to  disintegration  than  ordinary  carbon.  The  Castner 
alkali  process  was  originally  worked  with  carbon  electrodes 
graphitized  by  the  inventor's  own  process,  which  consisted 
in  packing  ordinary  carbons  in  carbon  dust,  and  subjecting 
them  to  a  white  heat  in  an  electric  furnace. 

Graphitized  carbon  electrodes,  as  manufactured  at 
Niagara  Falls,  under  the  Acheson  patents,  are  now  largely 
used  in  electrolytic  works. 

The  electrodes  used  in  the  manufacture  of  aluminium 
must  be  free  from  silica  and  silicates,  which,  if  present  as 
impurities,  lead  to  the  formation  of  silicon  fluoride,  by  re- 
action with  the  fluorine,  thus  robbing  the  bath  of  the  latter 
element.  Silica  also  is  liable  to  reduction  by  the  lower 
strata  of  aluminium  in  the  bath,  a  reaction  which  would 
destroy  the  purity  of  the  product.  Hydrocarbons  may  be 
present  in  the  carbon  electrodes  used  for  aluminium  manu- 
facture, and  have  no  deleterious  effect ;  the  carbon  should, 
however,  be  free  from  ash. 

In  carbide  manufacture,  on  the  other  hand,  the  presence 
of  hydrocarbons  and  silica  in  the  carbons  of  the  electrodes 
is  immaterial,  but  phosphate  impurities  are  debarred,  as 
they  lead  to  the  formation  of  calcium  phosphide,  with  the 
result  that  the  acetylene  gas  generated  from  the  resultant 

253 


ELECTRIC    FURNACES    AND 

carbide  is  rendered  impure  by  admixture  with  phosphoretted 
hydrogen. 

The  choice  of  suitable  carbon  electrodes  for  the  various 
electric  furnace  operations  detailed  in  this  book,  though 
seldom  thus  regarded,  is,  in  reality,  one  of  the  most  important 
features  in  electric  furnace  design,  contributing,  as  it  does, 
in  no  small  measure,  to  the  efficiency  of  the  process,  purity 
of  the  product,  and  last,  but  by  no  means  least,  as  a  refer- 
ence to  some  of  the  cost  statistics  already  given,  will  show, 
the  cost  of  the  process. 

Carbon  exists  in  various  polymeric  forms,  amorphous 
carbon,  sp.  gr.  1*7;  graphite,  sp.  gr.  2'25  ;  diamond,  sp.  gr. 
3'5  ;  and  various  other  equally  well-known  varieties. 

The  following  is  an  account  of  the  method  of  electrode 
manufacture  as  adopted  by  the  British  Aluminium  Company, 
and  furnished  by  Mr.  John  Sutherland  to  the  Electro-Chemist 
and  Metallurgist,  for  April,  1901. 

"  Carbon  electrodes  for  the  reduction  of  aluminium  may 
be  made  from  any  form  of  pure  carbon.  The  materials 
generally  used  by  the  various  carbon  works  are  retort  carbon, 
petroleum  coke,  soot,  anthracite,  and  Ceylon  graphite. 
The  crude  material  is  first  dried  or  roasted,  to  eliminate 
water,  or  any  organic  impurities,  and  then  ground  in  a  roller 
or  ball  mill.  The  ground  carbon  is  then  passed  to  the 
mixer,  where  it  is  thoroughly  mixed  with  anhydrous  taiy 
in  sufficient  quantity  to  make  it  bind  together  properly. 
The  mixers  in  use  are  various,  but  those  made  by  Werner 
and  Pfleiderer  seem  to  answer  best.  The  mixture  of  tar 
and  carbon  having  been  thoroughly  incorporated,  so  that 
each  grain  of  carbon  has  its  own  coating  of  tar,  is  ready 
for  formation  into  blocks,  which  is  effected  in  an  hydraulic 
press,  and  the  carbons  may  be  either  squirted,  or  pressed 
direct. 

"  The  next  step  in  the  process  is  the  baking  of  the  car- 
bons, which  is  done  in  a  furnace,  heated,  preferably,  by 
gaseous  fuel.  The  style  of  furnace  is  not  important,  pro- 

254 


THEIR    INDUSTRIAL   APPLICATIONS 

vided  the  goods  are  not  heated  or  cooled  too  quickly,  and  a 
high  temperature  is  obtained.  During  the  baking,  the 
carbons  are  packed  in  carbon  powder  to  protect  them  from 
oxidization. 

"  Good  carbons  should  emit  a  distinct  metallic  sound 
when  struck,  and  should  not  be  porous.  Unfortunately 
there  is  no  distinguishing  test  for  electrodes  ;  the  only 
means  to  determine  between  good  and  bad  ones  is  to  put 
them  through  the  ordinary  process  in  the  electric  furnaces, 
and  observe  their  behaviour  therein." 

Mr.  F.  A.  Fitzgerald,  of  the  International  Acheson 
Graphite  Company,  has  pointed  out  (Paper  before  Niagara 
Falls  Convention  of  American  Electro- Chemical  Society) 
that  in  both  electro-chemical  and  electro-metallurgical  pro- 
cesses, involving  the  use  of  carbon  electrodes,  the  deter- 
mination of  the  density  of  the  latter  is  an  important  point, 
in  that  the  general  efficiency  of  the  electrode  depends  upon 
the  nature  of  the  carbon,  and  consequently  on  its  density. 
It  is  desirable  to  know  both  the  real  and  apparent  densities, 
for,  having  given  these  two  quantities,  the  porosity  of  the 
electrode  can  be  arrived  at  by  calculation.  In  this  con- 
nexion, it  may  be  added  that  the  real  density  is  that  of  the 
carbon  composing  the  electrode,  whilst  the  apparent  density 
is  the  ratio  of  the  weight  of  the  electrode  to  its  volume  taken 
as  a  whole.  The  porosity  is  the  ratio  of  the  difference  of 
the  volume  of  the  electrode  taken  as  a  whole,  and  the  volume 
of  the  carbon  of  which  it  is  composed,  to  the  volume  of  the 
electrode  taken  as  a  whole. 

Owing  to  the  retention  of  air  by  amorphous  carbon  and 
graphite,  the  determination  of  the  real  density  is  not  easily 
accomplished.  Mr.  Fitzgerald  employs  a  volumeter,  fitted 
with  a  rubber  stopper  and  air-pump  connexion.  The  volu- 
meter, partly  filled  with  kerosene,  is  placed  in  a  water  bath 
and  a  reading  taken.  A  specimen  of  the  electrode  to  be 
tested  is  weighed  and  placed  in  the  volumeter,  which  is 
then  exhausted  of  air  by  means  of  the  pump.  When  the 

255 


ELECTRIC    FURNACES    AND 

maximum  attainable  vacuum  has  been  reached,  and  main- 
tained for  a  period  of  ten  minutes,  the  pump  is  disconnected 
and  a  reading  again  taken,  after  which  the  operation  is 
repeated  until  two  equal  consecutive  readings  are  obtained. 
Then  the  difference  between  this  last  and  the  original 
reading  of  the  volumeter  represents  the  actual  volume  of 
the  sample,  and  the  real  density  is  calculated  from  it. 

The  apparent  density  of  the  same  sample  is  now  deter- 
mined by  coating  it  lightly  with  shellac,  and  immersing  it 
in  water  in  the  volumeter,  which  then  indicates  the  apparent 
volume  by  displacement  ;  the  apparent  density  is  arrived 
at,  as  before,  by  calculation. 

Mr.  Fitzgerald  also  points  out  that,  in  view  of  the  fact 
that,  for  electro-metallurgical  purposes,  electrodes  of  pure 
graphite  are  preferable,  it  is  desirable  that  some  test  be 
instituted  to  determine  whether  such  electrodes  are  entirely 
composed  of  graphite,  or  whether  they  include  amorphous 
carbon  in  their  composition,  in  which  latter  case  they  are 
especially  subject  to  disintegration. 

Mr.  C.  M.  Hall,  the  inventor  of  the  aluminium  process 
which  bears  his  name,  has  devised  a  method  of  baking  carbon 
electrodes,  especially  those  intended  for  aluminium  manu- 
facture, in  an  electric  furnace  of  the  resistance  type.  To  this 
end,  the  carbons  are  disposed  either  in  horizontal  or  vertical 
rows,  around  a  carbon  core,  from  which  they  are  insulated, 
and  from  one  another  by  a  refractory  and  non-conducting 
powder,  such  as  bauxite,  purified  alumina,  magnesia,  etc. 
The  core  is  preferably  made  up  of  granular  charcoal  or 
coke,  but  a  fused  electrolyte  is  also  suggested. 

By  passing  a  suitable  current  through  the  core,  the  car- 
bons are  raised  to  a  temperature  of  1,647°  to  2,202°C.  =  3,000° 
to  4,000°F.,  very  little  current  actually  passing  through 
the  carbons  themselves.  The  following  data  are  suggested. 
A  core,  4  or  5  ft.  in  length,  and  12  by  30  in.  in  cross-sectional 
area,  requires  to  have  developed  therein  400  to  500  H,P., 
by  an  alternating  current  at  35-40  volts, 

256 


THEIR     INDUSTRIAL   APPLICATIONS 


SECTION    XIII 

EFFICIENCY  AND  THEORETICAL  CONSIDERATIONS 
The  efficiency  of  a  simple  electric  furnace  is  the  ratio  of 

the  heat  energy  of  the  electric  current  usefully  applied  to 

bring  about  the  operation  of  the  furnace,  to  the  total  heat 

energy  generated. 

The  heat  energy  usefully  applied  in  an  electric  furnace 

operation  is  absorbed  by  one  or  both  of  two  requirements, 

viz.  : — 

(1)  The  heat  energy  necessary  to  raise  the  temperature 
of  the  furnace  charge  to  that  point  at  which  the  desired 
reaction  occurs. 

(2)  The  heat  energy  taken  up  by  the  reaction  itself. 
Both  quantities  can  be  determined  by  calculation ;  the 

former,  from  the  mass,  specific  heats,  latent  heat  of  fusion, 
and  temperature,  whilst  the  latter  can  be  obtained  from 
known  thermo-chemical  data. 

The  efficiency  of  an  electric  furnace  is  governed  by  many 
factors,  for  the  greater  part  incidental  to  the  particular 
process  and  type  of  furnace  under  consideration.  Such 
general  determinants  as  size,  temperature  of  reaction, 
radiation,  disposition  of  terminals,  etc.,  may,  however, 
be  cited  as  controlling  factors,  especially  the  first  named, 
size,  or  dimensions  of  the  furnace. 

A  little  consideration  will  serve  to  show  the  importance 
of  this  point.  The  capacity  or  cubic  contents  of  a  furnace 
increase  approximately  as  the  cube  of  the  linear  dimensions, 
whilst  the  surface  available  for  radiation,  one  of  the  principal 
channels  through  which  heat  energy  is  lost  or  wasted, 

257  s 


ELECTRIC   FURNACES    AND 

only  increases  as  the  square  of  the  linear  dimensions ; 
in  other  words,  the  possibility  of  radiation  losses  does  not 
increase  in  direct  proportion  to  the  increase  in  capacity 
of  the  furnace,  so  that  a  large  furnace  is  far  more  efficient 
than  a  small  one.  The  general  tendency  therefore  should 
be  towards  an  increase  in  the  dimensions  and  capacity  of 
electric  furnaces,  only  limited  by  mechanical  or  other 
considerations. 

The  subject  of  electric  furnace  efficiency  was  most  ably 
dealt  with  by  Prof.  J.  W.  Richards,  Ph.D.,  in  a  Paper  read 
before  the  American  Electro-Chemical  Society  in  1902. 
For  purposes  of  discussion,  Prof.  Richards  classifies  electric 
furnaces  generally  under  two  main  heads,  viz. — 

(1)  Those  in  which  the  charge  is  simply  heated  without 
any  chemical  change  taking  place  ;  and 

(2)  Those  in  which,   beside  the  heating  of  the  charge, 
there  is  also  a  chemical  change. 

A  further  subdivision  is  based  upon  the  solid  or  fused 
condition  of  the  charge.  We  thus  have  four  sub-headings, 
viz. — 

(1)  Heating  without  fusion  and  without  chemical  change, 

(2)  „         with 

(3)  „         without     „         „     with  „ 

(4)  „         with          „         „         „  „  „ 

which  include  nearly  all  the  furnaces  and  furnace  operations 
described  in  this  book,  always  excepting,  of  course,  the 
electrolytic  section,  in  which  the  efficiency  of  the  electrolysis 
itself  is  a  controlling  feature,  and  must  be  duly  considered 
in  arriving  at  the  total  efficiency  of  the  furnace  or  process. 
As  an  example  of  No.  1  of  the  above  sub-headings,  we 
have  the  Acheson  graphite  furnace,  in  which  anthracite 
coal  is  converted  into  graphite.  Chemical  changes  do,  of 
course,  accompany  the  process,  in  the  shape  of  progressive 
formation  and  decomposition  of  carbides,  but,  from  the 
point  of  view  of  efficiency,  they  are  negligible,  in  that  the 

258 


THEIR    INDUSTRIAL    APPLICATIONS 

heat  energy  absorbed  exactly  counterbalances  that  evolved. 
The  actual  conversion  of  amorphous  carbon  into  graphite 
is  accompanied  by  the  evolution  of  heat,  and  therefore  once 
the  temperature  of  reaction  is  reached,  actually  assists  the 
current  in  bringing  about  the  desired  result. 

Roughly  speaking,  5,450  kgs.  of  anthracite  are  converted 
into  4,550  kgs.  of  graphite  by  an  expenditure  of  1,000  H.P. 
for  twenty  hours.  The  heat  actually  evolved  by  the  re- 
action itself  is  some  10  per  cent,  of  that  supplied  by  the  cur- 
rent ;  the  total  heat  energy  is  therefore  110  per  cent,  of  the 
heat  energy  available  from  the  current,  of  which  82-5  per 
cent,  is  utilized,  showing  an  efficiency  of  82-5-^110=75 
per  cent. 

Passing  on  to  a  consideration  of  the  allied  Acheson  pro- 
cess of  graphitizing  electrodes,  described  in  the  resistance 
furnace  section,  3,175  kgs.  of  electrodes,  embedded  in  the 
same  weight  of  granular  carbon,  call  for  an  expenditure  of 
1,000  H.P.,  the  efficiency  of  the  process  being  38  per  cent. 

Class  No.  2,  above,  is  exemplified  in  the  Jacobs  process 
of  fusing  calcined  bauxite.  The  process  is  one  of  simple 
fusion,  carried  out  in  a  cylindrical  crucible  or  hearth,  by  the 
heat  of  the  arc,  there  being  no  accompanying  chemical 
action.  The  efficiency,  with  a  1,360  kg.  charge,  is  74  per 
cent. 

Carborundum  manufacture  is  cited  as  an  example  in 
Class  3,  with  a  calculated  efficiency  of  76-5  per  cent. 

Under  Class  4,  the  manufacture  of  calcium  carbide  is  the 
best  known  example,  with  a  net  calculated  efficiency  of 
63  per  cent. 

The  principal  difficulty  attendant  on  the  calculation  of 
the  efficiency  of  many  electric  furnace  processes  is  the  pre- 
sent scarcity  of  data  concerning  the  specific  heat  of  the 
various  substances  treated,  at  high  temperatures.  An  ex- 
tensive scheme  of  research  in  this  direction  would  doubtless 
result  in  an  increase  of  reliable  data ;  it  is,  however,  a 
matter  of  time,  and,  until  this  information  has  been  gathered 

259 


ELECTRIC   FURNACES   AND 

together,    the    calculation    of    electric    furnace    efficiencies 
must  necessarily  be  approximate,  rather  than  exact. 

Summarizing  the  facts  at  his  command,  Prof.  Richards 
sets  down  a  general  figure  of  60-75  per  cent,  as  the  average 
commercial  efficiency  of  furnaces  varying  in  power  from 
200-1,000  H.P. 

Taking  the  case  of  the  Acker  process,  the  8,000  amperes 
consumed  in  each  furnace  should  yield,  theoretically,  287 
kgs.  of  caustic  per  twenty-four  hours.  In  actual  practice, 
with  a  yield  of  264  kgs.,  the  current  efficiency  is  93  per 
cent.  The  voltage  theoretically  required  for  the  electro- 
lysis of  fused  sodium  chloride  is  4-2,  therefore  the  total  or 
energy  efficiency  of  the  process  is  in  the  neighbourhood  of 
55  per  cent.  This  low  efficiency  is  in  part  due  to  the  heat 
energy  consumed  in  fusing  the  cold  salt,  and  bringing  it  up 
to  the  reaction  temperature. 

The  general  principle  and  disposition  of  a  commercial 
electric  furnace  would  not,  at  first  sight,  appear  to  lend 
itself  very  readily  to  theoretical  consideration  ;  neverthe- 
less, Mr.  F.  A.  Fitzgerald,  in  a  Paper  entitled  "  Note  on 
Some  Theoretical  Considerations  in  the  Construction  of 
Resistance  Furnaces,"  which  he  read  before  a  Niagara 
Falls  meeting  of  the  American-Electro-Chemical  Society  in 
1903,  treated  his  hearers  to  a  mathematical  disquisition  on 
the  theory  of  resistance  furnaces,  taking  as  his  subject  the 
well  known  Acheson  type,  used  in  the  manufacture  of 
carborundum,  graphite,  etc. 

In  all  these  furnaces,  the  electrical  resistance  is  a  variable 
quantity,  usually  diminishing  towards  the  end  of  a  run, 
and  it  is  obviously  impossible  to  effect  regulation  in  the 
interior  of  the  furnace,  except,  perhaps,  in  the  case  of  that 
particular  example  used  in  the  graphitizing  of  electrodes, 
where  some  little  adjustment  is  possible  by  varying  the 
spaces  between  neighbouring  piles  of  electrodes  under 
treatment. 

Regarding   the   distribution   of   heat   in   these    furnaces 

260 


THEIR    INDUSTRIAL    APPLICATIONS 

Fitzgerald  reasons  as  follows  :  If  a  cylinder  (core)  with 
radius,  pl  and  length  L,  is  kept  at  a  constant  temperature, 
0±,  the  quantity  of  heat,  Q,  passing  through  the  surrounding 
material,  the  inner  surface  of  which  is  at  the  temperature 
02  per  second,  is  Q=2<7rp1  LK  (#!  —  02)>  where  K  is  a 

constant.  Thus  —  fl,  —  02  —  o~~ 


If  the  material  outside  the  core  is  also  a  cylinder,  with  a 
radius  p2,  a  heat  conductivity  of  K15  and  a  temperature  at 

its  outer  surface  of  6Z,Q  =  — 


while  between  the  outside  of  the  cylinder  of  material  under 
treatment  and  the  walls  of  the  furnace,  the  passage  of  heat 

per  second  is  similarly  —  q  _        —  ^  3~  *' 


Pz 

or,  if  p2—p3=t,  and  is  very  small— 


84 
Now,  since  the  efficiency  of  the  furnace  is  9~?»   K'   and 

Mo 

03-04  must  be  kept  small  to  make  q  small.  Graphite 
and  electrode  furnaces,  however,  cannot  be  made  indefi- 
nitely large,  because  the  last  equation  shows  q  to  vary 
directly  as  the  product  of  L,  and  p2. 

In   the    case    of    the    carborundum    furnace,   the    chief 
equation  may  be  written  — 


To  make  the  largest  amount  of  carborundum,  Kt  must 
be  as  great  as  possible,  this  being  effected  by  having  the 
mixture  surrounding  the  core,  of  high  density,  for  then  the 
crystal  mass  formed  will  be  also  dense. 

261 


ELECTRIC    FURNACES    AND 

~  #3  should  also  be  large ;  but  the  latter  is  fixed  at  a 
temperature  just  below  that  of  the  formation  of  carborun- 
dum, while  #2  can  only  be  raised  to  a  point  short  of  its 
decomposition.  As  regards  the  outside  of  the  carborundum 
cylinder,  nothing  can  be  done  to  diminish  k,  but  03  —  04 
may  be  kept  small  by  having  a  good  thickness  of  raw  material 
always  present.  Since  the  value  of  p2  increases  with  the 
length  of  the  run,  a  point  will  eventually  be  reached  where 
q=Q  in  the  efficiency  equation,  so  that  a  time  comes  when 
no  more  carborundum  is  made.  To  work  efficiently,  the 
furnace  must  be  stopped  long  before  this  happens. 

According  to  MM.  Gin  and  Leleux  (Comptes  Eendus,  126, 
pp.  36),  the  temperature  of  the  arc,  when  employed  for 
heating  purposes,  may  be  computed  from  the  equation — 


where  p  is  the  resistance  of  the  envelope  of  gas, 

c  is  the  specific  heat  of  gas  per  unit  of  volume, 
$  is  the  sectional  area  of  the  electrodes, 
t  is  the  temperature  of  the  arc. 

Expressed  in  words,  this  formula  tells  us  that  the  tem- 
perature (t)  increases  directly  as  the  square  of  the  current 
density,  and  directly  as  the  ratio  of  the  total  resistance  of 
the  gaseous  envelope  to  the  specific  heat  per  unit  volume 
of  the  same. 

M.  Gin  has  since  supplemented  this  formula  by  others 
(Elelctrochemische  Zeitschrift,  May,  1902)  representing  tem- 
perature changes  and  efficiency  of  the  arc  furnace,  assuming, 
contrary  to  the  above  reasoning,  that  the  medium  sur- 
rounding the  electrodes,  in  the  neighbourhood  of  the  arc, 
is  a  conductor.  They  are  as  follows — 

Let  I  be  the  length  of  the  separating  medium 
s        „     diameter 

p       ,,     resistance  ,,  ,, 

c       ,,     specific    heat       ,,  ,,  based 

on  unit  volume. 

262 


THEIR    INDUSTRIAL    APPLICATIONS 

Then  the  amount  of  energy  converted  into  heat  in  unit 
time  is  C2R,  and  the  corresponding  heat  evolved  is 

I  /I  \  a 
A\s  ) 

If  the  arc  be  surrounded  by  a  heat  insulating  substance, 

the  equation  becomes   -  f  — ]  pis  —  cist,  from  which  it  will 

A\sJ 

be  seen  that  the  temperature  of  the  arc  in  the  mass,  will  in- 
crease in  proportion  to  the  square  of  the  current  density,  a 
condition  which  holds  good,  whether  the  intervening  medium 
between  the  electrodes  be  in  a  gaseous  or  fluid  state. 

M.  Gin's  formulae  for  calculating  the  temperature  of  a 
resistance  furnace  are  somewhat  complicated,  and  are, 
moreover,  based  on  certain  assumptions,  which  render 
results  more  or  less  approximate. 

In  applying  the  following  equations,  the  quantities  must 
be  expressed  in  gramme-calories. 

Let  Cs  be  the  mean  specific  heat  of  the  core,  or  other 

substance,  in  a  solid  state. 
Cf  be  its  latent  heat  of  fusion. 
Cl  be  its  mean  specific  heat  in  a  fluid  state. 
Or  be  the  heat  absorbed  as  a  result  of  the  chemical 

changes. 
P  be  the  weight  of  the  substance  passing  through  the 

furnace  in  unit  time,  when  in  full  operation. 
Tf  be  its  temperature  of  fusion. 

Let  Tr  be  the  temperature  at  which  the  reaction  occurs, 
and  2  be  the  total  superficial  area  of  the  exterior  of  the 

furnace  from  which  radiation  occurs. 
Then— 

EJ  =  M6  [P(CsTf  +  Cf  +  Cl   (Tr-Tf)    +  Cr)+K2STr]. 

From  this,  Tr  can  be  approximately  calculated.     Since 

K  Z  S  is  a  constant  for  one  type  of  furnace,  it  may  be  written 

K  ;  then,  omitting  CsTf,  the  equation  simplifies  down  to — 

EJ  =  M6  [P(Cf+Cr  +  Cl   (Tr-Tf) +KTr]. 

263 


ELECTRIC    FURNACES    AND 

whilst  the  effective  work  of  the  furnace  is  represented  by 

the  formula — 

P[  Cf  +  Cr  +  Cl  (Tr-Tf)] 

P  [Cf  +O+C1  (Tr-Tf )]+KTr, 

from  which  it  follows  that  the  lower  the  temperature  at 
which  the  desired  reaction  takes  place,  the  lower  will  be  the 
thermal  efficiency  of  the  furnace,  whilst  the  latter  will  in- 
crease in  proportion  to  the  heat  absorbed  by  the  various 
changes,  both  chemical  and  physical,  taking  place  in  the 
substance  of  the  furnace  charge  as  a  result  of  the  reaction. 


264 


THEIR    INDUSTRIAL    APPLICATIONS 


SECTION  XIV 

MEASUREMENT  or  FURNACE  TEMPERATURES 

It  is  necessary  for  the  sake  of  uniformity,  as  also  for 
purposes  of  research,  and  the  general  advancement  of 
scientific  knowledge  concerning  the  reactions  which  take 
place  in  the  electric  furnace  at  high  temperatures,  that 
some  convenient  and  reliable  means  be  provided  for  indica- 
ting, and,  if  necessary,  recording,  the  temperature  at  which 
any  particular  operation  is  being  carried  out.  The  provi- 
sion of  such  means  for  high  temperature  measurement  is 
by  no  means  so  simple  as  would  appear  at  first  sight. 

Owing  to  the  extremely  high  degree  of  heat  which  a 
furnace  of  the  electrical  variety  is  capable  of  evolving,  it 
is  impossible  to  introduce  anything  in  the  nature  of  a  ther- 
mometer structure  into  the  furnace  itself,  without  risk  of 
its  speedy  destruction,  either  by  fusion  or  combustion. 

The  ordinary  types  of  thermometer  which  depend,  for 
their  action,  on  the  expansion,  under  heat,  of  a  column  of 
liquid  are,  of  course,  out  of  the  question,  and  it  becomes 
necessary  to  fall  back  upon  some  method,  which  either  per- 
mits the  use  of  a  very  refractory  material  in  the  thermo- 
meter bulb  proper,  or,  for  still  higher  temperatures,  involves 
a  comparison  by  simple  observation,  between  the  tempera- 
ture of  the  furnace  and  that  of  a  known  standard,  which 
can  be  safely  manipulated  from  a  point  external  to  the 
furnace  itself. 

So  far  as  our  present  knowledge  carries  us,  the  only  two 
reliable  and  exact  methods  of  direct  furnace  temperature 
measurement  depend  upon  a  portion  of  the  apparatus  being 

265 


ELECTRIC    FURNACES    AND 

subjected  to  the  direct  heat  of  the  furnace,  and  their  range 
is,  in  consequence,  somewhat  limited.  Some  very  accurate 
and  valuable  records  of  temperature  have  nevertheless 
been  obtained  by  their  aid.  They  are  both  of  an  electrical 
character,  and  depend  for  their  action,  the  one  upon  the 
rise  in  electrical  resistance  of  a  short  length  of  platinum 
wire,  when  subjected  to  heat,  and  the  other,  upon  the 
electro-motive  force  set  up  at  the  hot  junction  of  a  refrac- 
tory thermo-couple. 

Much  valuable  work  in  the  perfecting  of  these  two  thermo- 
electric methods  of  high  temperature  measurement,  and 
the  means  for  accurately  indicating  and  recording  the 
temperatures  registered  by  them,  has  been  done  by  Profs. 
Callendar  and  Griffiths,  their  various  designs  being  worked 
out  and  manufactured  on  a  commercial  scale  by  the  Cam- 
bridge Scientific  Instrument  Company.  No  work  on  the 
industrial  application  of  high  temperatures  would  be  com- 
plete without  a  description  of  these  various  forms  of  appa- 
ratus, and  we  will  therefore  proceed  to  briefly  discuss 
them  in  their  bearing  on  electric  furnace  work. 

Of  the  two  methods  of  electric  thermometry,  just  con- 
sidered, the  resistance  method  yields  the  more  accurate 
results  up  to  about  600°C.=  1,112°F.  ;  whilst,  on  the  other 
hand,  the  thermo-couple  method  has  a  greater  range,  and 
permits  the  measurement  of  high  temperatures  in  very 
small  enclosures.  Its  comparatively  negligible  time  lag 
also  renders  it  especially  suitable  in  cases  where  a  con- 
tinuous record  of  rapidly  varying  temperatures  is  desired. 

Reverting  for  the  moment  to  a  consideration  of  the 
platinum  resistance  thermometer,  Professor  H.  L.  Callendar, 
in  an  article  in  the  Philosophical  Magazine  for  December, 
1899,  adduces  several  reasons  for  its  adoption  as  a  practical 
standard  for  high  temperature  measurements,  chief  among 
which  may  be  cited  the  facility  for  establishing  such  a 
standard  in  any  part  of  the  world,  it  only  being  necessary 
to  send  a  few  grammes  of  the  standard  wire  in  an  ordinary 

266 


THEIR    INDUSTRIAL    APPLICATIONS 

letter  to  any  desired  spot  in  order  to  reproduce  the  scale 
with  great  accuracy. 

A  paper  by  Mr.  H.  M.  Tory,  on  his  investigations  into 
the  probable  order  of  accuracy  obtainable  in  comparing 
high  temperatures  by  means  of  commercial  samples  of 
platinum  wire,  was  read  by  Professor  Callendar  before  the 
Physical  Society  on  June  22,  1900.  Five  different  samples 
in  all  were  subjected  to  comparison,  each  wire  being  directly 
compared  with  a  pure  platinum  standard  by  winding  the 
two  side  by  side  on  the  same  thermometric  tube.  It  was 
found  that  between  400°  and  1,000°C.=752°  and  1,832°F., 
the  fundamental  coefficients  of  the  wires  varied  within  40 
per  cent,  of  the  maximum  value,  but  that  the  temperatures 
registered  by  them,  when  calculated  on  the  platinum  scale 
by  means  of  the  ordinary  formula,  did  not  differ  by  more 
than  9°  at  1,000°C. 

Curves  were  plotted  from  the  results  obtained,  having 
the  platinum  temperatures  of  the  standard  wire  as  abscissae 
and  the  difference  between  the  temperatures  indicated  by 
the  two  wires  under  comparison,  as  ordinates.  Within  the 
limits  of  observation  these  were  all  straight  lines,  thus 
indicating  that  it  is  only  necessary  to  determine  two  con- 
stants in  order  to  compare  a  commercial  platinum  resist- 
ance thermometer  with  the  standard,  and  therefore  with 
the  scale  of  the  gas  thermometer  usually  accepted  as  a 
primary  standard.  These  two  constants  are  obtainable 
from  observations  at  the  boiling  point  of  sulphur  and  the 
freezing  point  of  silver,  permitting  the  construction  of  a 
practical  thermometric  scale,  which,  between  0°  and  1,000° 
does  not  vary  from  the  gas  scale  by  more  than  two  or  three 
degrees. 

In  No.  435,  Proceedings  of  the  Royal  Society,  C.  Chree 
treats  of  some  important  investigations  carried  out  at  Kew 
Observatory  with  a  view  to  determining  the  accuracy  of 
platinum  resistance  thermometry.  Six  of  these  thermo- 
meters were  tested  by  means  of  a  Callendar-Griffiths  resist- 

267 


ELECTRIC    FURNACES    AND 

ance  bridge,  and  no  less  than  thirteen  possible  sources  of 
error  were  discovered.  Among  the  principal  ones  are 
thermo-electric  currents,  set  up  at  the  various  junctions  ; 
heating  of  the  resistance  wire  by  the  battery  current  em- 
ployed in  taking  the  temperature  resistance  measurements  ; 
errors  in  the  temperature  coefficient  for  the  particular 
sample  of  platinum  wire  used  ;  insufficient  immersion  in 
the  substance  or  space,  whose  temperature  it  is  required 
to  measure,  and  excessive  time  lag,  or  slowness  in  acquiring 
the  temperature  of  the  surrounding  medium. 

The  effects  of  insufficient  immersion,  resulting  in  heat 
being  conducted  away  through  the  leads  and  external  con- 
nexions is,  for  commercial  work,  negligible,  though  it  may, 
if  the  total  immersion  be  less  than  10  c.m.,  amount  to  as 
much  as  0'01°C.,  or  even  more. 

The  time  lag  calls  for  more  consideration,  especially  if 
the  thermometer  tube  be  only  inserted  in  the  furnace  at 
intervals,  and  thus  not  left  continually  immersed. 

The  six  thermometers  tested  were  found  to  take  from 
four  to  five  times  as  long  in  acquiring  the  temperature  of 
the  surrounding  furnace  atmosphere,  as  a  mercurial  thermo- 
meter. 

So  important  a  value  has  the  platinum  resistance  method 
of  high  temperature  measurement  acquired  of  late  years, 
that  in  1887  Professor  Callendar,  by  dint  of  elaborate  and 
careful  investigations  which  he  then  made  into  the  pos- 
sibilities of  this  method  of  thermometry,  introduced  the 
scheme  of  "  Platinum  Temperatures,"  or  the  Platinum 
Scale,  which  is  a  standard  for  the  platinum  resistance 
method  of  thermometry,  just  as  the  Fahrenheit,  Centigrade, 
and  Reaumur  scales  are  standards  for  the  previously  exist- 
ing mercurial  instruments.  These  platinum  temperatures 
are  obtained  from  the  formula  — 


where  pt  is  the  platinum  temperature,  corresponding  with 

268 


THEIR    INDUSTRIAL    APPLICATIONS 

the  ohmic  resistance  R  of  a  given  wire,  the  resistance  of 
which  at  100°C.  and  0°C.=212°F.  and  32°F.  are  Rl  and  Ro 
respectively. 

The  researches  of  Professors  Callendar,  Dewar,  Fleming, 
Griffiths  and  others  show  that  this  law  holds  good  for  all 
temperatures  between  -200°C.  and  1,300°C.  =  -328°F. 
and  2,372°F.,  irrespective  of  the  extremes  and  rapid  varia- 
tions of  temperature  to  which  the  wire  may  be  subjected, 
provided  it  be  carefully  annealed  ;  and  that  the  platinum 
wire  invariably  offers  the  same  resistance  at  the  same 
temperature. 

So  far,  however,  as  the  actual  variation  of  resistance  with 
temperature  goes,  the  law  appears  to  be  of  a  complicated 
nature. 

Among  others,  J.  D.  Hamilton  has  investigated  this 
subject,  and  in  the  Philosophical  Magazine  for  December, 
1897,  he  suggests  the  formula — 

(R+«)2  =  p  (t+b), 

where  a,  p,  and  b  are  constants,  and  R  and  t  the  resistance 
and  temperature  respectively.  This  most  nearly  repre- 
sents the  results  hitherto  obtained.  The  constants  have, 
however,  to  be  individually  obtained  for  each  wire  by  a 
series  of  careful  observations. 

Messrs.  Crompton  &  Co.,  of  Chelmsford,  in  this  country, 
and  Messrs.  Hartmann  &  Braun,  of  Frankfort,  both  manu- 
facture a  direct  reading  electrical  thermometer  based  on 
the  platinum  resistance  principle.  The  indicator  itself, 
resembles  a  direct-reading  ohm-meter,  and  consists  of  two 
intersecting  coils,  mounted,  and  capable  of  rotation  in  a 
non-homogeneous  magnetic  field.  A  standard  resistance 
of  known  value  is  included  in  the  circuit  of  one  coil,  whilst 
the  other  is  connected  with  the  coil  of  the  resistance  thermo- 
meter. The  latter,  for  high  temperatures,  is  constructed, 
as  usual,  of  platinum,  whilst,  for  lower  degrees  of  heat,  a 
"  nickelin "  wire  is  employed.  The  scale  is  graduated 

269 


ELECTRIC    FURNACES    AND 

directly  in  degrees,  and  has  a  range  extending  up  to  1,200°C., 
the  highest  temperature  that  can  be  measured  by  its  aid. 

For  regular  and  constant  use  an  open  scale  in  the  neigh- 
bourhood of  the  most  usual  temperatures  under  measure- 
ment can  be  obtained  by  a  suitable  adjustment  of  the  shape 
of  the  pole  pieces. 

The  current  required  to  actuate  the  indicator  is  only 
0*03  ampere  at  5  volts. 

Messrs.  Siemens  Bros,  also  manufacture  a  conven- 
ient form  of  platinum  resistance  pyrometer,  in  which  the 
resistance  wire  is  wound  upon  a  refractory  cylinder,  and 
protected,  for  the  greater  part  of  its  length,  by  an  iron 
tube  ;  being  additionally  safeguarded  at  its  active  extre- 
mity, which  is  exposed  to  the  direct  heat  of  the  furnace,  by 
a  platinum  shield.  An  increase  in  the  resistance  of  the 
platinum  spiral,  from  10  ohms  to  44'9  ohms,  corresponds 
with  a  rise  in  temperature  from  14°C.  to  1,205°C.=58°F. 
to  2,204°F.  Two  methods  of  reading  the  indications  are 
provided  by  the  makers,  either  one  of  which  can  be  adopted. 
One  consists  of  a  differential  galvanometer  and  a  set  of 
resistance  coils,  which,  used  in  conjunction  with  a  battery, 
give  the  required  resistance  in  ohms,  the  corresponding 
temperature  being  read  off  a  scale  supplied  with  the  instru- 
ment. The  other  apparatus  consists  of  a  Wheats  tone 
bridge  combined  with  a  D'Arsonval  galvanometer,  the 
variable  arm  of  the  former  being  arranged  in  the  form  of  a 
circle,  traversed  by  a  sliding  contact  arm,  carrying  an  index 
which  moves  over  a  circular  scale  calibrated  to  read  directly 
in  degrees  Fahrenheit. 

The  use  of  the  thermo-couple  for  high  temperature  ther- 
mometry  was  proposed  as  far  back  as  1826  by  the  late  M. 
Becquerel.  He  adopted  it  for  the  measurement  of  the 
underground  temperature  in  the  Natural  History  Museum 
of  Paris  ;  an  iron-copper  couple  was  employed,  one  junction 
of  which  was  situated  in  the  underground  area,  whose 
temperature  was  desired,  whilst  the  other  was  immersed 

270 


THEIR    INDUSTRIAL    APPLICATIONS 

in  a  bath,  the  temperature  of  which  was  capable  of  regula- 
tion either  by  artificial  heating  or  cooling,  and  could  be 
measured  by  means  of  an  ordinary  mercurial  thermometer. 
A  galvanometer  was  included  in  the  thermo-couple  circuit, 
and  the  temperature  of  the  bath  regulated  until  its  deflection 
became  zero,  a  sure  indication  that  both  junctions  were 
at  the  same  temperature.  The  temperature  of  the  bath, 
and  consequently  of  the  underground  space,  was  then 
measured  by  means  of  an  ordinary  mercurial  thermometer. 

M.  Henri  Becquerel,  the  grandson  of  the  above,  has 
suggested  a  more  direct  method  of  using  the  thermo-couple 
for  this  purpose,  which  he  designates  as  the  "  Sliding  Scale  " 
method.  A  high  resistance  D'Arsonval  galvanometer  is 
included  in  the  circuit  from  the  thermo-couple,  and  has  its 
scale  graduated  to  read  directly  in  degrees  of  temperature. 
In  setting  up  the  instrument  to  indicate  the  temperature 
of  a  given  enclosure,  such  as  a  furnace,  the  scale  is  so  placed 
that  the  zero  or  undeflected  position  of  the  galvanometer 
mirror  indicates  upon  it  the  temperature  of  the  room  in 
which  it  is  placed,  and  which  has  been  previously  deter- 
mined by  means  of  an  ordinary  mercurial  thermometer. 
Any  subsequent  deflection  then  gives  the  required  tempera- 
ture of  the  other  junction  directly,  and  without  the  neces- 
sity for  calculation,  or  for  keeping  the  cold  junction  at  zero 
by  immersion  in  an  ice  bath. 

In  Comptes  Bendus,  April  28,  1902,  M.  D.  Berthelot  gives 
some  very  interesting  and  practical  information  respecting 
the  calibration  of  thermo-couples  for  use  in  high  temperature 
thermometry.  According  to  him,  the  cheapest  and  most 
satisfactory  couple  is  formed  of  platinum,  in  conjunction 
with  a  10  per  cent,  alloy  of  platinum  and  iridium.  To  ensure 
regularity  in  the  curve  of  comparisons,  the  calibration  should 
be  carried  out  in  an  atmosphere  of  air,  nitrogen,  or  carbon 
dioxide  gas. 

Between  the  temperatures  of  400°  and  1,100°C.=  752° 
and  2,012°F.,  the  curve  denoting  the  relationship  between 

271 


ELECTRIC    FURNACES   AND 

Log.  E.M.F.  and  Log.  temperature  is  to  all  practical  intents 
and  purposes  a  straight  line. 

M.  Berthelot  employed,  for  his  limiting  temperatures, 
the  melting  point  of  zinc  (419°C.=  786°F.)  and  the  melting 
point  of  gold  (1,064°C.=  1,947°F.),  the  latter  being  deter- 
mined automatically  by  the  insertion  of  a  piece  of  that  metal 
between  the  elements  at  the  hot  junction,  and  reading  the 
E.M.F.  at  the  instant  before  the  circuit  is  interrupted  by 
the  fusion  of  the  gold. 

The  Reichsanstalt  apparatus  for  calibrating  thermo- 
couples for  high  temperature  measurement  is  described 
in  the  portion  of  the  book  dealing  with  laboratory  furnaces. 

Mr.  H.  J.  Robinson,  in  letters  to  the  Electrical  Review, 
March  6  and  April  17,  1903,  calls  attention  to  some  of  the 
drawbacks  incidental  to  the  use  of  thermo-electric  pyro- 
meters as  at  present  constructed,  and  points  out  how  they 
may  be  in  part  eliminated.  His  experience  appears  to  have 
been  gained  in  the  use  of  platinum,  platinum-rhodium,  or 
iridium  thermo-couples,  made  up  of  wires  "018  in.  in  dia- 
meter, threaded  through  porcelain  insulators,  and  protected 
by  a  steel  tube,  merging,  at  its  outer  end,  into  a  water-cooled 
terminal  box.  In  this  type  of  pyrometer,  the  primary 
trouble  was  experienced  at  the  hot  junction,  which  is  effected 
by  fusing  the  ends  of  the  two  wires  together. 

Mr.  Robinson  found  it  more  conducive  to  a  constant 
reading,  when  the  ends  forming  the  hot  junction  are  tightly 
twisted  together  for  about  a  quarter  of  an  inch,  and  fused 
or  not  fused,  in  addition,  as  the  case  may  be.  Another 
source  of  trouble  was  the  rapid  deterioration  of  the  wires, 
owing  to  the  hot  furnace  gases  entering  the  tube  ;  this  was 
circumvented  by  an  extra  sheathing  of  iron  steam  pipe, 
slipped  over  the  steel  protecting  tube,  and  its  open  extre- 
mity welded  up.  This  latter  procedure  also  reduces  the 
trouble  consequent  on  the  liability  of  the  platinum  to 
become  brittle  or  "  short  "  with  continued  usage.  In  this 
connexion,  he  has  found  heating  the  wire  white  hot  in  air 

272 


THEIR    INDUSTRIAL   APPLICATIONS 

a  number  of  times,  by  passing  a  suitable  current 
through  it,  to  be  efficacious.  A  120- volt  supply  was  utilized, 
the  current  being  switched  on  and  off  about  twenty  times, 
which  removed  all  tendency  to  brittleness.  The  wire  should 
be  well  cleaned  before  replacing  in  its  mounting. 

Consequent  on  Mr.  Robinson's  letters  came  a  communica- 
tion from  Mr.  S.  Weiss  containing  a  suggestion  that  the  steel 
protecting  tube,  and  water-cooled  terminals  be  dispensed 
with  altogether,  and  the  pyrometer  mounting  made  entirely 
of  fire-clay,  some  3  or  4  ft.  in  length,  a  form  of  construction 
which,  in  the  writer's  opinion,  is  impracticable  on  the  score 
of  weakness  and  liability  to  fracture.  Mr.  Weiss  further 
states  that  such  a  fire-clay  tube  may  be  rendered  impervious 
to  furnace  gases  by  washing  it  over  with  a  mixture  of  pure 
kaolin  and  water,  mixed  to  the  consistency  of  cream. 

The  possibilities  of  thermo-electric  pyrometry  are  limited 
by  the  fusing  temperature  of  the  metals  employed  in  the 
construction  of  the  thermo-couples,  and  by  the  fact,  recently 
pointed  out  by  Nernst,  that  all  substances,  commonly  em- 
ployed as  refractory  insulators,  become  good  electrical  con- 
ductors at  high  temperatures. 

As  we  travel  higher  in  the  temperature  scale,  we  have  to 
fall  back,  as  already  stated,  upon  other  methods,  all  of 
which  are  founded  on  more  or  less  direct  comparison  with 
a  negotiable  standard  situated  outside  the  furnace. 

One  of  the  simplest  and  most  ingenious  of  these  methods, 
which  is  also,  unfortunately,  limited  as  to  its  range  of 
applicability,  consists  in  the  comparison,  by  observation, 
of  the  degree  of  incandescence  of  an  electric  lamp  filament 
with  that  of  the  heated  interior  wall  of  the  furnace,  an 
inspection  opening  being  provided  for  the  purpose  in  the 
wall  of  the  latter. 

The  apparatus  in  general  resembles  a  telescope,  mounted 
on  a  light  tripod,  and  placed  with  its  axis  in  line  with  the 
opening  in  the  furnace  wall.  A  small,  low-voltage,  incan- 
descent electric  lamp,  fed  with  current  by  two  or  more  dry 

273  T 


ELECTRIC    FURNACES    AND 

cells,  or  small  accumulators,  is  fitted  within  the  tube  of  the 
telescope,  the  current  through  it,  and,  consequently,  its 
degree  of  incandescence,  being  regulated  by  means  of  a 
rheostat  and  switch. 

The  method  of  taking  a  temperature  observation  consists 
in  viewing  the  incandescent  filament  of  the  lamp  against 
the  glowing  background  of  the  interior  furnace  wall ;  if  the 
filament  appear  black,  or  dark,  then  its  condition  of  incan- 
descence, and  consequently  its  temperature,  is  lower  than 
that  of  the  furnace  ;  whereas  if  it  appear  as  a  white  or  light 
line,  its  temperature  is  higher  than  that  of  the  furnace 
interior.  By  means  of  the  regulating  resistance  and  switch, 
the  current  through  the  lamp  is  regulated  until  the  filament, 
as  viewed  against  the  incandescent  furnace  wall,  apparently 
disappears.  This  signifies  that  the  two  are  in  an  equal  state 
of  incandescence,  and,  consequently,  that  their  temperatures 
are  equal.  The  actual  temperature  of  the  filament  is  then 
read  off  from  a  scale,  previously  prepared  by  experiment, 
which  gives  the  relation  between  the  current  passing,  as 
registered  on  an  ammeter  included  in  the  circuit,  and  the 
temperature. 

The  range  of  this  ingenious  device  is  limited  to  1,980°C. 
=  3,600°F. 

The  optical  pyrometer  has  lately  been  elaborated  and 
constructed  on  a  more  practical  basis  by  Dr.  H.  Wanner. 
It  is  being  manufactured  and  marketed  by  Messrs.  Emier 
&  Amend,  of  New  York,  and  is  applicable  to  temperatures 
of  4,000°C.  =  7,232°F.,  or  above. 

The  following  is  Dr.  Wanner's  description  of  the  appa- 
ratus and  principle  involved — 

"  The  law,  as  established  experimentally,  permits  at 
least  for  a  certain  group  of  glowing  bodies  (the  so-called 
theoretically  '  black  bodies '),  measurement  up  to  the 
highest  temperatures.  When  a  compact  body  is  heated, 
the  rays  emanating  from  the  same  may  be  observed  by 
the  human  eye,  and  the  body's  colour  will  change,  with 

274 


THEIR    INDUSTRIAL    APPLICATIONS 

rising  temperature,  from  dark  red  to  light  red,  to  yellow, 
and  to  bright  white.  This  means  that  at  first  mainly  red 
rays  are  observed,  to  which,  at  the  higher  temperatures, 
the  other  spectrum  colours,  orange,  yellow,  etc.,  are  added, 
until  the  rays  appear  white. 

"  In  analyzing  the  rays  by  a  prism  it  is  found  that  with 
the  rise  of  temperature,  some  single  colour,  for  instance, 
red,  undergoes  a  rise  in  intensity,  which  can  be  measured 
progressively  with  a  specially  constructed  photometer. 
If  we  know  the  law  for  the  mutual  relation  between  the 
determining  factors  (the  temperature  and  the  light  intensity 
of  the  single  colour,  and  its  wave  length)  we  are  enabled  to 
measure  high  temperatures  by  the  photometric  measure- 
ment of  the  light  intensity  of  a  certain  colour. 

"  The  apparatus  to  be  applied  is  therefore  a  photometer, 
containing  at  the  same  time  a  prism,  to  separate  a  single 
colour.  A  spectrum  is  produced  in  the  ordinary  manner 
with  the  aid  of  a  slit,  lenses,  and  a  prism,  from  which,  by 
means  of  a  diaphragm,  the  light  of  a  certain  wave  length 
is  separated,  and  the  measurement  of  the  light  intensity 
is  made  by  polarization.  To  that  part  of  the  apparatus 
which  faces  the  radiation  to  be  examined,  a  small  incan- 
descent lamp  is  attached,  the  light  of  which  is  used  for 
comparing  the  intensity  of  the  light  to  be  measured. 

"  On  looking  through  the  apparatus  one  observes  the 
circular  field  of  vision,  divided  into  two  halves  (like  in  a 
one-half  shade  sugar- testing  polariscope),  one  of  which  is  illu- 
minated by  the  small  incandescent  lamp,  and  the  other  by 
the  light  of  the  glowing  body  being  examined.  Both  halves 
of  the  field  show  red  colour.  On  turning  the  eye-piece 
containing  the  Nicol  prism  both  halves  of  the  field  of  vision 
can  be  easily  brought  to  equal  intensity,  and  on  a  circular 
scale  the  number  of  degrees  are  read.  The  actual  tempera- 
ture is  found  from  a  table  which  accompanies  each  instru- 
ment. The  temperatures  given  on  the  table  have  been 
calculated  by  means  of  the  law  mentioned  before. 

275 


ELECTRIC   FURNACES   AND 

"  The  entire  procedure  is  so  simple  that  it  can  be  readily 
learned  by  any  foreman  or  intelligent  workman  within  a 
short  time.  The  whole  apparatus  is  30  c.m.  long,  built 
like  a  telescope,  and  can  be  easily  handled  without  a  sup- 
port. It  does  not  matter  how  great  the  distance  is  from 
which  the  measurements  are  taken,  if  only  the  field  of 
vision  is  properly  illuminated  by  the  light  emanating  from 
the  body  to  be  examined. 

"  The  exactness  of  this  new  method  depends  solely  on 
the  accuracy  of  the  observer,  and  on  the  degree  to  which 
the  body  under  test  approximates  what  is  called  in  the 
theory  of  radiation,  a  '  black  body.'  Errors  due  to  lack  of 
experience  of  the  observer  are  practically  eliminated,  for 
various  parties,  who  have  been  asked  to  take  measurements, 
and  who  used  this  apparatus  for  the  first  time,  have  obtained 
the  same  correct  results.  The  nearest  approximation  to 
the  theoretical  '  black  body  '  are  the  insides  of  the  closed 
furnaces,  as  muffles,  etc.,  the  glow  of  which  is  observed 
through  a  small  opening,  which,  however,  must  not  be 
covered  by  glass  or  mica  during  the  measurement.  The 
measured  temperature  is  equal  to  the  real  one  within  a  few 
degrees." 

Another  method  of  high  temperature  determination, 
which  verges  more  nearly  on  direct  measurement  than  the 
foregoing,  is  based,  in  principle,  on  Stefan's  law,  which  runs 
to  the  effect  that  the  radiation  from  an  absolutely  black 
body  is  proportional  to  the  fourth  power  of  its  absolute 
temperature.  By  an  "  absolutely  black  body  "  is  meant, 
in  this  case,  one  which  receives  and  retains  all  the  heat 
imparted  to  it,  and  only  gives  it  out  again  by  radiation, 
and  not  by  reflection  from  its  surface. 

Kirchoff  has  shown  that  the  interior  walls  of  an  enclosure, 
such  as  a  furnace,  which  are  at  a  high  uniform  temperature, 
behave  as  an  absolutely  black  body,  according  to  the  above 
definition,  and  its  existence  as  such  is  not  materially  altered 
by  the  presence  of  the  small  orifice  necessary  for  taking 

276 


THEIR    INDUSTRIAL    APPLICATIONS 

the  temperature  observation.  Given,  then,  an  absolutely 
black  body,  in  this  case  a  portion  of  the  incandescent  wall 
of  the  furnace,  it  is  possible  to  concentrate,  and  measure,  a 
certain  small  definite  proportion  of  the  radiated  heat,  and 
by  this  means  determine  the  temperature. 

The  apparatus  for  achieving  this  in  practice  also  takes 
the  form  of  a  species  of  telescope,  with  an  objective  of  fluor- 
spar. The  latter  substance  is  chosen  for  this  purpose  by 
the  inventor,  M.  Fery,  because  its  absorption  of  radiant 
heat  is  very  small,  and  the  consequent  error  from  loss,  due 
to  the  passage  of  the  rays  through  it,  is  correspondingly 
small.  In  actual  practice,  the  sensitiveness  of  the  device 
is  decreased  by  about  10  per  cent. 

The  radiant  heat  thus  concentrated  by  the  fluor-spar 
objective  is  received  upon  the  junction  of  a  miniature 
thermo-couple  placed  at  the  focus  ;  the  resulting  E.M.F.  is 
measured,  and,  by  simple  computation,  gives  the  required 
temperature  of  the  furnace.  The  lens  is  disposed  for 
parallel  rays,  and  a  diaphragm  cuts  off  all  but  a  certain  pre- 
determined cone,  which  is  allowed  to  reach  the  thermo- 
couple, thus  rendering  the  device  independent  of  its  dis- 
tance from  the  furnace. 

M.  Fery's  apparatus  has  been  standardized  by  comparison 
with  a  Le  Chatelier  pyrometer,  and  exhibited  an  error  well 
below  1  per  cent.,  between  temperatures  of  914°C.  and 
1,450°C.=1,677°F.  and  2,642°F.  respectively.  Owing  to 
the  minuteness  of  the  mass  to  be  heated  (less  than  1-1 00th 
of  a  milligramme)  there  is  practically  no  time  lag,  the  appa- 
ratus following  quick  variations  in  the  temperature  under 
measurement  with  surprising  accuracy.  Neither  has  any  diffi- 
culty been  experienced  with  the  zero,  which  is  very  constant. 

The  temperature  of  the  positive  arc  carbon,  as  measured 
by  this  device,  was  found  to  be  3,490°C.=  6,314°F. 

M.  C.  Fery  has  also  experimented  with  a  somewhat 
similar  method  of  high  temperature  measurement  by  radia- 
tion, which  is  based  on  Wien's  complex  law. 

277 


ELECTRIC    FURNACES    AND 

Am  T=A,  where  X  is  the  wave  length,  T  the  absolute 
temperature,  and  m  refers  to  the  maximum  energy  radiated 
at  a  particular  wave  length. 

This  gives  the  radiation  in  terms  of  any  chosen  wave 
length,  instead  of  the  total  radiation  as  in  the  previous 
method  founded  on  Stefan's  law. 

M.  Fery  has  compensated  the  complexity  of  Wien's 
formula  by  a  method  of  considerable  ingenuity.  He 
reduces  the  standard  radiation  to  equality  with  that  under 
measurement  by  interposing  an  acute-angled  prism  of 
absorbent  glass,  in  the  path  of  the  rays.  This  prism  is  so 
displaced  as  to  interpose  varying  thicknesses.  The  absorb- 
ing power  of  the  prism  also  follows  a  formula  of  the  Wien 
type,  and  is  such  that  the  displacement  is  inversely  pro- 
portional to  the  temperature  under  measurement.  The 
latter  is  thus  read  off  from  the  degree  of  displacement  of 
the  prism,  when  the  two  radiations  have  been  equalized. 

By  this  method,  temperatures  of  3,867°C.  and  3,897°C.= 
6,992°F.  and  7,046°F.,  in  red  and  green  light  respectively, 
have  been  obtained  for  the  positive  carbon  of  the  arc. 
There  is  thus  a  discrepancy  between  these  values,  and  the 
3,490°C.=  6,314°F.  obtained  by  the  previous  radiation 
method,  and  it  is  accounted  for  by  the  fact  that  carbon 
does  not  behave  as  an  absolutely  black  body  at  the  tem- 
perature of  the  arc. 

As  far  back  as  1858  Balfour  Stewart  demonstrated  that 
the  emissivity  and  the  absorptive  power  of  a  body  at  a  given 
temperature,  are  equal  for  any  radiation.  This  is  known 
in  England  as  Stewart's,  and  on  the  Continent  as  Kir- 
choff's,  law,  having  been  independently  proved  by  the 
latter. 

By  "  absorptive  power  "  is  meant  that  portion  of  the  total 
radiation  received  by  a  surface,  which  is  absorbed,  whilst 
the  "  emissivity  "  of  a  body  at  a  given  temperature,  for 
any  given  radiation,  is  the  ratio  of  the  quantity  of  that 
radiation  which  it  emits,  to  the  quantity  of  the  same  radia- 

278 


THEIR   INDUSTRIAL   APPLICATIONS 

tion  emitted  by  an  ideal  black  body  at  the  same  tempera- 
ture and  under  the  same  conditions. 

In  1879  Stefan  evolved  the  law  which  is  known  by  his 
name,  and  is  to  the  effect  that  the  total  radiation  from  any 
ideal  black  body  varies  as  the  fourth  power  of  the  absolute 
temperature.  In  1884,  a  theoretical  proof  of  this  law  was 
furnished  by  Boltzmann,  who  based  his  reasoning  on  one  of 
Maxwell's  fundamental  laws  regarding  the  electro-magnetic 
theory  of  light,  viz.,  that  a  beam  of  light  exerts,  in  the  direc- 
direction  of  propagation,  a  pressure,  per  unit  of  area,  equal 
to  the  energy  in  unit  volume  of  the  radiations.  Following 
closely  on  the  deductions  of  Boltzmann,  came  two  laws, 
formulated  by  Wien,  and  expressed  by  the  equations  :  XT  =  a 
constant,  or  \mT=a>  constant,  and  EwT~5=  a  constant. 
The  former,  which  is  known  as  the  "  Law  of  Displacement," 
has  it  that  any  monochromatic  radiation  is  moved  towards 
the  shorter  wave  length  by  a  rise  of  temperature. 

It  has  remained  for  MM.  Lummer  and  Pringsheim  to 
supply  the  connecting  link  between  theory  and  practice, 
which  they  have  recently  done,  by  proving  experimentally 
the  truth  of  these  various  relations  between  radiation  and 
absolute  temperature.  These  investigators,  taking  the 
mean  of  several  readings,  have  proved  the  constant,  for  an 
ideal  black  body  to  be  \mT=  2,940. 

These  two  investigators  (Berichte  der  Deutschen  Physi- 
Icolischen  Gesettschaft,  I.,  1903)  state  the  three  laws  relating 
to  black  radiation  to  be  as  follows — 

(l)/000EXdX=:0-T4  (Stefan-Boltzmann  Law). 

(2)  AmT=A  (contained    in  Wien's    Displacement 

Law). 

(3)  EmT5=B. 

where  EXdX  is  that  portion  of  the  black  radiation  contained 
between  X  and  X  +  dX  at  the  temperature  T  of  the  gas  ther- 
mometer scale  ;  Xm  is  the  wave  length  for  which,  at  this 

279 


ELECTRIC    FURNACES    AND 

temperature,  the  emissive  power  EX,  in  the  normal  spectrum, 
reaches  its  maximum  Em ;  m  is  the  maximum  energy 
radiated  at  a  particular  wave  length,  whilst  <r,  A,  and  B  are 
constants,  determinable  with  sufficient  accuracy. 

By  means  of  a  specially  constructed  carbon  tube  resist- 
ance furnace,  the  interior  of  which  represented  the  theo- 
retical black  body,  and  the  radiation  from  which  was  mea- 
sured simultaneously,  by  several  different  methods,  including 
a  surface  bolometer,  spectrum  bolometer,  and  spectrum 
photometer,  the  above  experimenters  have  succeeded  in 
verifying  the  foregoing  laws,  and  rendering  them  applicable 
to  absolute  temperature  measurement  up  to  2,300°C.= 
4,172°F.,  thus  extending  the  possible  range  of  correct 
thermometry  by  about  1,000°C.=  1,832°F. 

In  order  to  apply  the  laws  of  radiation  to  the  exact 
measurement  of  high  temperatures,  all  that  is  necessary  is 
to  expose  a  bolometer  or  radiation  meter  to  an  orifice  in  the 
heated  furnace  cavity,  which  is  equivalent  to  an  "  absolutely 
black  body,"  and,  by  this  means,  measure  the  radiant  energy 
given  off  by  it. 

K.  Ferrini  has  suggested  the  application  of  calorimetric 
methods  to  the  measurement  of  high  temperatures,  the 
latter  being  calculated  from  results  obtained  with  a  calori- 
meter. The  following  table  gives  the  number  of  kilogramme 
calories  necessary  to  raise  the  temperature  of  a  kilogramme 
of  platinum,  or  nickel,  from  zero,  or  freezing-point,  to  a  given 
temperature — 


280 


THEIR  INDUSTRIAL  APPLICATIONS 

FINAL  TEMPERATURE.  CALORIES  ABSORBED  BY  1  KILOGRAMME. 

DEGREES  C.  PLATINUM.                                     NICKEL. 

100 3-23 12 

200 6-58 24 

300 9-95 37 

400 13-64 50 

500 17-35 63-5 

600 21-18  ......  75 

700 25-13 90 

800 29-20 103 

900  ......  33-39 117-5 

,000 37-70 134 

,100 42-13 — 

,200 46-65 

,300 51-35 — 

,400 56-14 

,500 61-05 . 

,600 66-08 

,700 71-23 

1,800 76-50 

Then  the  following  formulae  apply  for  the  computation 
of  the  temperature.  Let  ra  be  the  weight  of  the  metal, 
M  that  of  the  water,  ^  the  initial,  and  t2  the  final  tempera- 
ture of  the  water,  c  the  specific  heat  of  the  metal  at  t2,  and 
Q,  the  heat  required  to  cool  the  body  from  the  unknown 
temperature,  T  down  to  zero,  and  we  have — 
ra  (Q-c^-y, 

whence  Q  =  ct2  +       (t2  —  tj 

Having  thus  determined  Q,  the  value  of  T  may  be  ascer- 
tained from  the  table  within  100  degrees.  If  greater  accu- 
racy be  required,  the  following  equations  are  applicable — 

For  platinum — 

T +  52-84  T-Q-|-6=0. 

For  nickel — 

1+Q 


T  = 


13 

The  results  obtained  are  said  to  be  correct  between  700° 
and  800°C.=  1,292°,  and  1,472°F.,  whilst  the  errors  intro- 
duced when  the  temperatures  are  exceeded,  are  negligible. 

281 


ELECTRIC   FURNACES    AND 

For  experimental,  or  laboratory  work,  the  method  is 
worthy  of  consideration,  but  would  appear  altogether  too 
complicated  for  adoption  on  a  commercial  scale. 

There  is  another  way  of  estimating  high  temperatures, 
which  can,  however,  hardly  be  regarded  in  the  light  of 
temperature  measurement,  in  that  it  is  of  assistance  only 
in  giving  visible  indication  of  the  fact  that  a  certain  pre- 
determined temperature  has  been  reached. 

It  was  devised  by  Prof.  Seger,  as  a  rough,  practical 
test  for  the  pottery  manufacturer,  to  determine  the  tem- 
perature of  his  baking  ovens,  and  consists  of  the  well-known 
"  Seger  Cones,"  or  "  Pyramids."  As  the  result  of  a  series 
of  exhaustive  fusion  experiments,  Prof.  Seger  suc- 
ceeded in  producing  a  series  of  systematic  mixtures  of  pure 
silicates,  aluminates,  etc.,  each  having  a  different  melting 
point,  and  each  mixture  differing,  in  its  melting  point 
some  20°  or  30°C.,  from  the  one  next  above  or  below  it  in 
the  scale.  A  series  of  fifty-eight  different  mixtures  or 
compositions  were  thus  worked  out,  with  fusing  points, 
which  varied  from  dull  red,  590°C.  =  1,094°F.,  to  the 
melting  point  of  platinum,  1,850°C.=  3,362°F.,  in  steps 
of  20°  or  30°  C.=68°  or  86°  F.  These  mixtures,  moulded 
into  conical  or  pyramidal  form,  are  known  as  "  Seger  Cones," 
and  the  method  of  using  them  to  ascertain  when  a  certain 
pre-determined  temperature  has  been  reached,  is  to  place 
one  or  more  of  the  cones,  which,  on  the  Seger  scale  of  tem- 
peratures, represent  most  nearly  the  desired  temperature 
at  different  points  of  the  furnace  cavity,  suitably  supported 
and  protected  by  refractory  slabs. 

When  the  fusing  temperature  of  the  composition  of  which 
the  cone  is  constructed  has  been  reached,  it  softens,  and 
collapses,  its  upper  portion,  or  apex,  curving  over.  The 
degree  of  curvature,  if  the  temperature  be  not  unduly  ex- 
ceeded, is,  to  the  experienced  eye,  an  additional  gauge  of 
the  exact  degree  which  has  been  reached.  Observation 
holes  in  the  walls  of  the  furnace,  and  in  line  with  the  cones, 

282 


THEIR    INDUSTRIAL    APPLICATIONS 

are,  of  course,  essential,  and  should  be  protected  by  mica 
to  prevent  indraughts  of  air  from  vitiating  the  results. 

The  following  table  represents  the  chemical  composition 
of  Seger  cones  over  a  limited  portion  of  the  scale,  between 
1,330°C.=:2,4260F.  and  1,530°C.  =  2,786°F.,  inclusive— 


10  '      '      '          "  1<0  Al2°3  10Si°2- 


?  CaOJ   l'2  A1*°3  12  Si 
12  '      '      '      (o'.7CaO|    1<4  A1*°3  14 


13  •    •    •          cao    1'G  M*°*  16  Si°2     •    •    1'390 

14  '      '      •          '  1<8  A12°     18  Si°2       •      '      1'410 


15  •      '      '      {o.7  Cao}  2-1  A12°3  21  Si°2       •      •      M30 

16  '      '      '      {o^7  CaOJ    2'4  A1^°3  24  Si°2       •      •      1'450 


17  '      '      '  j    2'7  ^°3  27  Si°2       •      • 


iQ  vajv2v^|  „  ,     . ,  o  „,    s-o  14.00 

i  a  .  .         .         S  f\n   r^<-iO  f                 -^J2     3              oiv^2  •         •         A,«*{*VJ 

10  •  •      •      (n^n'nl  3'5  A1203  35  Si02  .      .     1,510 

20  . 


For  full  particulars,  the  reader  is  referred  to  the  original 
pamphlet,  describing  the  cones,  which  was  published  by 
the  Thonindustrie  Zeitung  (Berlin). 

Although  essentially  a  rough  and  ready  method  of 
recording  high  temperatures,  the  system  has  one  great 
advantage  ;  any  workman,  of  average  intelligence,  can  be 
entrusted  with  the  carrying  out  of  temperature  investiga- 
tions by  its  aid. 


283 


INDEX 


Acheson    Group    of    Electric    Fur- 
naces, 36 

—  Carborundum  Furnace,  36 

—  Graphite  Furnace,  43 

—  Furnace  Terminal,  247 
Acker  Sodium  Process,  199 
Advantages,  Relative,  of  Arc  and 

Resistance  Principles,    13 

—  Principal,  of  Electric  Furnace,  15 
Alloys  of  Iron  and  Steel,  156 

—  Aluminium,  159 
Aluminium,   Manufacture  of,    176 

—  Haber     &     Geipert's     Experi- 

ments, 181 
-  Heroult  Process,  183 

—  Heroult  Furnace,  185 

—  Hall  Process,  186 

—  Price  of,  182 

—  Theoretical     Considerations     in 

Manufacture  of,  188 
Alundum,  214 
Application  of  Electric  Furnace  to 

Scientific  Research,  228 
Arc  Furnaces,  21 

Theoretical  Action  of,  26 

Arndt's  Calcium  Process,  209 
Arsenic  Smelting,  146 

—  Furnace,  147 
Artificial  Graphite,  43 

—  History  of,  44 
Aschermann     Chromium     Process, 

155 

Barium  Cyanide,  215 
Baryta,  214 

Becker  Glass  Furnace,  172 
Blount's  Carbide  Furnace,  70 
Borchers'  Furnace,  87 

—  Resistance  Furnace,  30 

—  and    Stockem's    Calcium    Pro- 

cess, 206 

—  and  Stockem's  Strontium  Pro- 

cess, 208 

Bradley  Furnace,  82 
Bronn  Glass  Furnace,  174 

Calcium,  Borchers'  Process,  206 

—  Arndt's,  209 

—  Manufacture  of,  206 


Calcium  Carbide  Manufacture,  58 
-  Carbide,    Purification    of,    63 

—  Temperature      of       Formation 

of,  64 

—  Quality  of,  65 

—  Current    used    in    Manufacture 

of,  65 

—  Raw  Materials  in  Manufacture 

of,  67 

—  Furnace,  Blount's,   70 

Willson's,  72 

Gin  &  Leleux,  73 

Parks',  75 

Maxim,  76 

—  —  Zimmerman,  78 

Roller,  79 

Morley,  79 

Nikolai,  80 

Horry,  81 

Bradley,  82 

Kenevel,  84 

Pictet,  85 

Borchers,  87 

—  —  Memmo,  89 

Parker,  93 

Frohlich,  95 

Cowles,  96 

Contardo,  97 

King,  98 

Deutsche   Gold   und-    Silber 

Scheide  Anstalt,  99 
Calcium  Cyanide,  215 
Carbon  Bisulphide  Furnace,  55 
Carborundum,  36 

—  Furnace,  Acheson,  36 

—  for  lining  Furnaces,  39 
Chromium,  Preparation  of,   155 
Classification  of  Electric  Furnaces, 

10 

Coal,  Peat,  Jebsen  Process,  53 
— :  —  Bessey  Process,  55 
Coke  Purification,  52 
Combustion  Furnace,  241 
Combination  Furnace  Processes,  217 
Comminution  of  Metals,  161 
Conley  Smelting  Furnace,  128 
Contardo  Smelting  Furnace,  130 

—  Carbide  Furnace,  97 
Copper  Smelting,  144 


285 


INDEX 


Cores,  Tests  of  Resistance  Furnace, 

29 
Cowles,  early  experiments,  7 

—  Furnace,  31 

—  Carbide  Furnace,  96 

—  Zinc  Furnace,  151 

—  Sodium  Process,  156 
Crucible  Furnace,  Howe,  225 

Darling  Sodium  Process,  205 
De  Chalmont  Furnace,  21 
Deductions,   Scientific,    19 
Definition  of  Electric  Furnace,  1 
De  Laval  Smelting  Furnace,  112 

—  Zinc  Furnace,  152 
Denbergh  Arc  Furnace,  23 
Dental  Muffle,  Hammond,  226 
Deutsche  Gold  und  Silber  Scheide 

Anstalt  Carbide  Furnace,  99 
Distillation  of  Zinc,  151 
Dorsemagen  Zinc  Process,  154 
Dumoulin  Resistance  Furnace,  31 

Early    History    of    Electric     Fur- 
nace,  1 

Eddy  Tube  Furnace,  240 
Efficiency,  Furnace,  257 
Eimer  Electric  Oven,  226 
Electric  Furnace,  Definition  of,  1 
Electrodes,  251 

—  Graphitizing,  50 

—  Hall  method  of  Baking,  256 
Electrolytic  Furnace  Processes,  176 

Faure  Furnace,  7 

Ferro -Manganese,    Simon    Process, 

210 

Fischer  Sodium  Process,  204 
Franklin  Smelting  Furnace,  117 
Frohlich  Carbide  Furnace,  95 

—  Resistance  Furnace,  34 
Furnace,  Electric,  Definition  of,  1 
Siemens,  2 

Moissan,  5 

Faure,  7 

Temperature  attainable  in,  8 

Classification  of,  10 

Principal  Advantages  of,  15 

Arc,  21 

Three  Phase,  Advantages 

of,  25 

Carbonizing  Lamp  Fila- 
ments in,  25 

Resistance,  27 

Application  of  Polyphase 

Currents  to,  34 


Furnace,   "  Induction  "  35 

Acheson  Group,  36 

for  Graphitizing  Electrodes, 

51 
Baking  Carbon  Articles  in, 

52 

Coke  Purification  in,   52 

Tube,  235 

-  Terminals,  246 

-  Electrodes,  251 

-  Efficiency,  257 

Gibbs  Resistance  Furnace,  32 
Gin  Steel  Furnace,  112 
—  Process,  113 

-  &  Leleux  Carbide  Furnace,  73 
Girod  Resistance  Furnace,  33 
Glass,  Manufacture  of,  170 

-  Furnace,  Shade,  170 

—  —  Henri  vaux,  172 

Becker,  172 

Voelker,  172 

Bronn,  174 

Graphite,  Artificial,  43 

—  Furnace,  Acheson,  43 

—  Artificial,  History  of,  44 
Conditions     for     Formation 

of,  48 

Graphitizing  Electrodes,  50 
Guntz  Tube  Furnace,  244 

Hall  Aluminium  Process,  186 
Hammond  Dental  Muffle,  226 
Harmet  Smelting  Furnace,  115 
Henri  vaux  Glass  Furnace,   172 
Heraeus  Tube  Furnace,  243 
Heroult  Smelting  Furnace,   120 

-  Steel  Process,  122 

—  Aluminium  Process,    183 
-  —  Furnace,  185 

History,    Early,    of    Electric    Fur- 
nace, 1 

-  of  Artificial  Graphite,  44 
Horry  Carbide  Furnace,  81 
Howe  Crucible  Furnace,  225 
Hulin  Sodium  Process,  198 

Induction  Furnace  Principle,  35 
Iron  and  Steel  Production  in  Elec- 
tric Furnace,  107 

—  Processes,  110 

—  Alloys,  156 

Irvine  Phosphorus  Furnace,  167 


Keller  Smelting  Furnace,  113 


286 


INDEX 


Kenevel  Carbide  Furnace,  84 
King  Carbide  Furnace,  98 
Kjellin  Steel  Process,  138 

—  Furnace,  139 
Roller  Arc  Furnace,  25 

—  Carbide  Furnace,  79 

Laboratory  Furnaces,  221 
Lead,    Production    of    in  Electric 
Furnace,  211 

Magnesium,  Production  of,  211 
Machalske  Phosphorus  Process,  168 
Magnetic  Field,  Monk's  Patent,  16 
Manganese,  Manufacture  of,  209 
Maxim  Carbide  Furnace,  76 
Measurement  of  Furnace  Tempera- 
ture, 265 

Memmo  Carbide  Furnace,  89 
Metals,  Pulverization  of,  161 
—  Lomax  Method,  162 

Bary  Method,  162 

Miscellaneous  Electric  Furnace  Pro- 
cesses, 214 
Moissan's  Researches,  4 

—  Furnace,  5 

Molybdenum,  Preparation  of,  155 
Morley  Carbide  Furnace,  79 
Muffle,  Hammond  Dental,  226 

—  Weiss  Resistance,  227 
-  Winter  Resistance,  227 

Nickel,  Production  of,  155 
Nikolai  Carbide  Furnace,  80 

Optical  Pyrometer,  274 
Oven,  Eimer  Electric,  226 

Parks  Carbide  Furnace,  75 
Parker  Carbide  Furnace,  93 
Patten  Arc  Furnace,  24 
Peat  Coal,  Jebsen  Process,  53 

Bessey  Process,  55 

Phoenix  Process,  190 
Phosphorus,  Manufacture  of,  165 

—  Furnace,  Readman-Parker,  165 

-  Irvine,  167 

Machalske,  168 

Pictet  Carbide  Furnace,  85 
Platinum  Resistance  Thermometry, 

268 
Polyphase  Currents,  Application  of 

to  Electric  Furnaces,  34 
Potter  Tube  Furnaces,  236 
Pradon  Carbide  Furnace,  66 
Pulverization  of  Metals,  161 


Purification  of  Calcium  Carbide,  63 

—  Coke,  52 

Readman-Parker  Phosphorus  Fur- 
nace, 165 

Relative  Advantages  of  Arc  and 
Resistance  Principles,  13 

Researches,  Sir  Wm.  Siemens',  2 

—  Moissan's,  4 

—  Application  of  Electric  Furnace 

to  Scientific,  228 
Resistance  Furnaces,  27 

Cores,  Tests  of,  29 

Walls    of,  33 

Ruthenberg  Smelting  Furnace,  124 

—  Process,  The,  126 


Salgue's  Zinc  Process,  154 
Scholl  Sodium  Process,  204 
Scientific  Deductions,  19 
Seger  Cones,  282 
Shade  Glass  Furnace,  170 
Siemens'  Researches,  2 

-  Furnace,  2 
Silicides,  216 
Siloxicon,  40 

—  Furnace,  41 
Simon  Smelting  Furnace,  115 

-  Ferro-Manganese  Process,  210 
Smelting  with  Electrolysis,  Chlor- 
ine, 190 

—  Furnace,   De  Laval,    112 
Gin,  112 

—  —  Processes,   113 

-  —  Keller,  113 

-  Simon,  115 

—  —  Harmet,  115 

-  Franklin,  117 
Weber,  119 

Heroult,  120 

Ruthenberg,  124 

Conley,  128 

Contardo,  130 

Stassano,  133 

Kjellin,  139 

Tone,  143 

Smelting,  Copper,  144 

—  Arsenic,  146 

—  Zinc,  151 

Sodium  and  Caustic  Soda,  197 

—  Process,  Cowles,  156 

Vautin,  197 

Hulin,  198 

Acker,  199 

Castner,  202 


287 


INDEX 


Sodium  Process,  Scholl,  204 

Fischer,  204 

Darling,  205 

Stassano  Process,  The,  131 

—  Furnace,  133 
Statistics,  General,  18 

Steel   Production  in  Electric  Fur- 
nace, 107 
Strontium,  Manufacture  of,  206 

Borchers  Process,  208 

Swinburne- Ash  croft  Process,  190 

Temperature  Attainable  in  Electric 
Furnace,  8 

—  of  Formation  of  Calcium  Car- 

bide, 64 

—  Measurement  of  Furnace,  265 
By  Radiation  Methods,  276 

—  —  by     Calorimetric     Methods, 

280 

by  Seger  Cones,  282 

Terminal  Connexions  and  Elec- 
trodes, 246 

—  Acheson,  247 

Thermo-Electric    Pyrometry,    270 
Theoretical    Action    of    Arc    Fur- 
nace, 26 

—  Considerations,  257 

Theory  of  Aluminium  Manufac- 
ture, 188 

Three-Phase  Currents,  Advantages 
of,  25 

—  Furnaces,  Memmo,  89 


Tone  Smelting  Furnace,  143 
Tube  Furnaces,  235 

Potter,  236 

Terminal     Connexion     and 

Mounting  of,  237 

Revolving,  238 

on  Nernst  Principle,  239 

Eddy,  240 

Heraeus,  243 

Guntz,  244 

Tungsten,  Preparation  of,  155 

Vanadium,  Preparation  of,  212 
Vautin  Sodium  Process,  197 
Voelker,  Arc  Furnace,  25 
—  Glass  Furnace,  172 

Walls  of  Resistance  Furnaces,  33 
Weber  Smelting  Furnace,  119 
Weiss  Resistance  Muffle,  227 
Westman  Arsenic  Furnace,  147 
White  Stuff,  39 
Willson  Carbide  Furnace,  72 
Winter  Resistance  Muffle,  227 


Zimmerman  Carbide  Furnace,  78 
Zinc,  Distillation  of,  151 

—  Electrolytic  Extraction  of,  212 

—  Furnace,  Cowles,  151 
De  Laval,   152 

—  Process,  Salgues,   154 

—  —  Dorsemagen,    154 


But!:r  &  Tanner,  The  Selwood  Printing  Works,  r>ome,  and  London. 


288 


MINERAL  TEEHNOLQGY  LIBRARY 
UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

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JUL  1 4  1990 
1954 


LD  21-100m-9,'48(B399sl6)476 


